Libertarianism is okay as an ideal, but the simple truth is that there are some things we need government for. One thing I greatly disagree with the libertarians on is the need for public education. My public education has provided me with countless opportunities and an excellent general education. I do not believe that private schools can offer the sort of programs that my 2800 student high school offered, such as a nationally competitive marching band, 100-piece orchestra, Amnesty International club alongside a Conservative Student Union, auto shop alongside vector calculus and differential equations, three levels of football teams, a club that has mentally disabled children hanging out with unhandicapped classmates, a Christian club alongside a Jewish club and Muslim club, a Black Student Union and MECHA...the list could go on. I think that private schools by necessity specialize in one thing or the other, and public schools provide more things to more people. This is not even adressing the issue of low-income families who rely on public education.
Other things we need government to provide: public land stewardship, fire fighting service, public parks and swimming pools, corporate oversight, stewardship of public resources (i.e. radio frequencies, water resources), providing independent researchers with money, etc.
Finally, on a purely ideological level, I strongly disagree with the libertarian party's stand on gun control. To sum this argument up: if guns were outlawed, only outlaws would shoot their kids accidentally.