No, no, no. I do not care to spend my time arguing with libertarians. Those people love the sound of the last word far too much for my tastes.
But if there were a couple of tangible problems with them, I'd place:
1. that they always want revolutionary change rather than baby steps (in an "all or nothing" game, they have too little power to get it all, and that leaves "nothing" everytime),
2. they consistently misinterpret the Constitution (e.g., they think that the phrase "general welfare" has ZERO meaning),
3. they constantly cry wolf about nebulous, unnamed freedoms that they think they've lost
at the top of my list of problems with them.
They are idealists. They argue for a perfect world, and I find that pursuit unrealistic.