I friend of mine is an ardent Libertarian. I am highly sympathetic, but he doesn't believe me.
Mainly, I believe in Liberty whenever possible because no human system can be trusted to regulate human activity completely perfectly. If you don't really know how to regulate human activity, experience shows me that it's better to leave people alone to do their own thing. This does free them to do new and interesting and terrible things.
But my friend is basically an anarchist, as near as I can tell, and believes we can depend on selfish motives to supply all human needs. I, too, am a fan of Ayn Rand, which I've talked about in this space more than once but I'm too lazy to link right now, but I'm not a fanatic about it.
Rand is very convincing. But I think once you get a little distance from the work it's pretty easy to see the problems with it. I believe the core of her beliefs are excellence, but trying to implement it in a perfect idealistic fashion is quite, quite mad.
It's strange. Libertarians don't trust anyone to have any governmental function, but they trust everyone enough to regulate themselves to the point of making a "perfect" society.
I trust people on the whole, but come on, have you never met a real asshole?