Thinking about the problems of government policy in any depth makes it obvious simple solutions aren't possible. These folks are unwilling to accept that - they believe they are wiser and more able than any human that came before them. Since they're ubermen they believe that the muddling through humans have done for hundreds of thousands of years is no longer necessary -- if only people would follow their enlightened example all would be well. They don't seem to understand that their ideas have been tried and found wanting -- they're convinced they are the only people who really "get it."
I'll give libertarians credit for one thing -- they've made me far more conservative with their radicalism. Seeing how their simple solutions would fail terribly in the real world has made it easier to see how some of my own preferred policies probably wouldn't work as I intended were they adopted. They also have a pretty good understanding of the futility of the government attempting to regulate private consensual economic relations between individuals -- only an authoritarian state could do it effectively.
I just wish more libertarians could accept that they are just one of many ideological traditions that we NEED to make good policy. Not one of the many ideologies is absolutely right -- part of the genius of a properly-functioning democracy is that it forces the kind of collaboration between competing viewpoints that gives us the best possible policy.