Before you become a Libertarian activist, please consider....

• Libertarianism is utopian in its vision of society, and as history has shown, fighting for utopias often leads to the exact opposite.   It is a utopian vision because there has never been a completely free market with an attendant minimal government incapable of taxing or regulating business, as envisioned by libertarians, in any modern industrial society.  This is because such a weak, underfunded minimal government would be incapable of protecting individual rights, not to mention other responsibilities sensibly left today to government, and would quickly degrade to a plutocracy or gangster capitalism.  The inevitable corruption and injustice within such a society would likely inspire a revolution with potentially unlibertarian results.
• Libertarianism is profoundly anti-democratic.  Libertarians give lip service to democracy but their denunciation of government and their quest to privatize everything says otherwise.  You cannot have a strong democracy supporting individual liberty, including property rights, in a culture that celebrates a contempt for public service, idolizes the rule of the wealthy, reduces the decisions of what can be voted on to largely minor, inconsequential matters, and sneers at the suggestion that public -- that is government -- endeavors or places have any importance for building a healthy civil society.   Modern democratic governments in North America, Europe, Asia, and Australia have created the freest, most prosperous societies in world history -- many with extensive welfare states, and all with a hefty dose of government regulation of the economy.  Libertarians, despite their intentions, by pursuing their utopian free market ideals, are inviting less freedom and even more injustice into our world.  
• Political and economic freedom needs strong federal, state, and local governments.  A smoothly functioning market requires strong government to even exist.  The libertarian paradigm of government power opposing market power is a cartoon caricature.   The real struggle today,  is between strong democratic government with relatively free markets vs. the rule of thugs, whether in the form of gang warfare or government dictatorships.
• Libertarianism is at odds with the spirit of the Declaration of Independence and the U.S. Constitution.  Libertarians only see liberty, as in freedom from government, in our country's founding documents.  They are blind to the equal importance in our country's founding principles of strong government "to enforce these rights" --  that is freedom made manifest through a government capable of efficiently enforcing laws protecting individual freedom, including the rights of minorities, property rights, trial by jury, the right to petition government, environmental protection, etc.   
• Libertarians are largely clueless to the necessity of equality in order for liberty to actually mean something for all Americans, regardless of race, religion, sexual preference, wealth, or status - to unite us as a people.  They act as if the only choice we have before us is, at one extreme, a material equality enforced by a communist dictatorship, or, at the other extreme, a rejection of equality as the enemy of liberty.  Libertarians assume the later and advocate the dismantling of the government safety net--Social Security, Medicare, minimum wage laws, etc. -- and all government assistance to anyone, regardless of need.  In their intellectual paranoia, libertarians are blind to the many positive effects of government wealth redistribution programs, including maintaining a strong middle class.  A weak middle class with the majority dominated by the political power of an extremely wealthy few (sound familiar) is a recipe for corruption and eventual dictatorship.  Libertarians, if they really believe in freedom in the real world, should celebrate the welfare state and democratic governance.
• Libertarians have little to say in how to fight racism, sexism, or homophobia in America. While libertarians firmly reject racism and sexism and openly embrace different sexual preferences, marriage practices, etc., they do not see government as having a positive moral role in eradicating the worse effects of bigotry.  As an example, libertarians oppose the Civil Rights Act of 1964, and still do to this day, since they believe that government has no right to dictate how business owners run their businesses, including who they can serve or hire. Libertarians hold an almost child-like belief that their "free market" will somehow make everything better over time, including eradicating prejudice, since, libertarians argue, prejudice is not profitable. To their credit, libertarians do point out the decidedly racist consequences of drug law enforcement in the U.S. where blacks and hispanics are three times as likely to be jailed for illegal drug sales or possession than whites.  But to all the racist policies in effect over the past century and a half enforced by white landowners, white-owned banks and businesses, and state legislatures intent on keeping African Americans "in their place," libertarians have only hollow words of support and encouragement since, above all, for libertarians, property rights must be respected.  For the same reason, libertarians oppose any equal pay for equal work statutes to address the unequal treatment of women in our culture and are cool to any government action in support of the LGBT community.  
• Libertarianism unintentionally provides a moral veneer to white racism in America.  Property rights were used by white slaveholders in the south and, after the Civil War, by racists intent on keeping federal government authorities from intervening in support of racial or religious minorities.  "Protecting our rights" has been the excuse of bigots from George Wallace to the present day.  Libertarians have no problem with diversity, racial or otherwise and thus provide a kind of radical chic to pro-capitalist ideology that can make radical property rights seem "cool" to the newly initiated.  So it might seem unfair to accuse the libertarian movement of some kind of complicity with racists.  But the congruence of white racist views with libertarian views goes well beyond a shared opposition to anti-discrimination laws and legislation and should make libertarians question their priorities.  Libertarian historiography is profoundly anti-federal government in ways that American racists would agree with.  For example, libertarian historians regard Lincoln as a tyrant and support the old Confederacy's secession from the United States.  It is no coincidence that the racists within modern American conservatism also avidly defend a libertarian brand of free market ideology.   So where does the racism end and libertarianism begin?  Who can tell? 
• Libertarianism has a schizophrenic relationship with the best spirit of our times.  On one hand, libertarians do celebrate diversity and innovation.  They do not fear world trade or open immigration and are severe critics of militarization and war.  Libertarians are strong defenders of free speech and a free press.  To this extent, libertarianism seems to be a philosophy for our future - one where our planet is truly becoming one world, with deeply integrated markets, entwined with the music, art, and ideas from everywhere, made real by instant communication with every corner of the globe.  And then libertarians go crazy in the opposite direction -- insisting with puritanical vehemence that markets must be "free" of all government regulation or subsidy.  Libertarians are firmly opposed to laws prohibiting child labor or government agreements protecting wildlife.  Government protections for consumers, workers, indigenous tribes, or the environment are rejected by libertarians.   Any hint at world governance, either through the United Nations or by other intergovernmental organizations are condemned as the beginnings of a much-feared world government.   Only world "governance" via nondemocratic private organizations and corporate boardrooms is acceptable to libertarians - a real recipe for dystopia.
• Libertarians are helpless before the threat of human-caused climate change.  Since libertarians reject government regulation as coercive, they believe they must reject any attempts by governments to impose restrictions on fossil fuels, or any government programs to address the consequences of a changing climate, regardless of the science.  Their only course is to either a) reject the science altogether, b) argue that higher CO2 levels are a net benefit to the world, or c) feign helplessness.  There is no greater illustration today of the idiotic consequences of a puritanical adherence to libertarian radical capitalist doctrine, then the proud know-nothingness on this issue by today's libertarians and radical free market conservatives
• Libertarianism is inadvertently anti-science.  We are witnessing an Age of Discovery unlike any in human history.  The space programs of the United States, Russia, and Europe have opened our eyes to the wonders of the cosmos as never before.  U.S. government efforts to map the ocean floor and to understand and even predict motions within our earth and in our atmosphere have led to unparalleled excellence in severe storm and climate forecasting.  Our Centers for Disease Control and its counterparts in other countries, financed by tax dollars, has saved countless lives.  The internet was initially developed as a government effort.  Yet libertarians would reject all of this.  They would counter, ever hopeful in their utopianism, that the free market would of course explore the heavens, forecast the weather for everyone, cure disease, and invent the internet, all without taxation.  The burden of proof is on the libertarians.  But what a wonder of scientific discoveries and endeavors to condemn and throw away on a utopian (or dystopian) dream.
• A libertarian society, even if momentarily realized, would be less free than our current messy American democracy.  Government makes us freer not only by enforcing and maintaining individual rights, as mentioned above, but in many other ways.  For example, prior to Social Security, Medicare, and Medicaid, the elderly were often the poorest segment of our population.  That's no longer the case thanks to the government. And because our elderly are better taken care of, imagine how that frees up their lives and those of younger generations.  We still have to look after our parents and older relatives, of course, but we are no longer solely responsible for their welfare, and that relieves many of us of an enormous potential burden.  Then there's travel on the open road.  Remember, libertarians would do away with taxpayer-funded public roads, including the interstate highway system.  Private transportation companies would replace some of these services but always with a cost passed on to the consumer.   So libertarians would "free" us to use toll roads -- thanks a lot.  How about affordable college?  Whether through the G.I. Bill, direct loans, or government funding of public universities, government has made college available to those from low and middle incomes.  Libertarians would do away with all of those programs.  There are so many ways that government frees up opportunities for the poor and middle class, that to argue for the abolition of most government, as libertarians do, is to argue for less freedom and opportunity.
• Libertarians are opposed to national parks, and for that matter state and local parks, whatever has to be funded by tax dollars.   I agree with Ken Burns that the national parks are indeed one of America's "greatest ideas," and I challenge any libertarian to come up with something better.  Libertarians will point to Nature Conservancy's protection of endangered ecosystems, yes, but the Grand Canyon, Yellowstone, Yosemite, owned by a private entity whether a corporation or nonprofit?  These are places for all Americans, not just for some board of directors ever sensitive to more profits from wealthier patrons, to control.  Libertarians would counter that "the people" do not control the National Parks, only government bureaucrats do.  Not true -- the National Park Service, like any government bureaucracy, is extremely sensitive to political pressures from politicians and their constituents.   It can be slow and sloppy yes, but it has worked wonderfully.  The evidence is in the parks -- magnificent beauty and incredible ecosystems that we have preserved over time.  Libertarians would trash these for their dystopian dream.
• The embrace of an extreme form of individualism within the American libertarian movement culture encourages alienation and nondemocratic impulses.  I can perhaps illustrate this best with an example -- take two policemen.  One works for a city police department and is paid out of the public treasury.  The other works for and receives his wages from a private security company.   Both do their jobs well.  Libertarians would tend to see both as equivalent in status, with perhaps a nod to the private cop as being more ethical, since he would not be taking tax dollars.   In contrast, a people embracing a healthy democratic spirit would view the former as having a far greater responsibility.  The city policeman does not just work for the city, but for the people of that city.  He has sworn an oath to serve and protect.  The private policeman's ultimate duty is to the corporation that employs him; but for a public servant, it must be otherwise.  Every public servant is working for the people of their community, state, and or country.  If you listen for it you will hear this sentiment.  I have. I have heard it from policemen, park rangers, weather forecasters for the National Weather Service, NASA astronauts, and our men and women in the armed forces.  From the local to the national level, there is something about public service that carries a greater responsibility than being in the private sector.  And it is this sentiment - "I am working for the people of America" -- that daily "greases the wheels" of our democracy.  Does this public service sentiment prevent corruption?  Of course not, but it carries a strong moral incentive not to engage in corrupt activities, an incentive that cannot be matched in the private sector except by the ethical constraints an employee imposes on his or herself.  For the private sector employee, their behavior is an individual matter than might affect their company and its clients.  For the public sector employee, there is a communitarian responsibility to all the people within their jurisdiction.  Corruption violates that trust.   However, public service "does not compute" in the libertarian paradigm.  Libertarians are complete cynics when it comes to public service.  They even mock it.  And by doing so, libertarians help to erode yet another foundation of the only form of government--democratic government-- that has brought us, however imperfectly, the freedom and prosperity many of us enjoy today.