> However, in my experience they seem to try to vastly simplify many issues by waving their hands and talking about the non-aggression principle as if that automatically solves everything. The truth is, while there may be laws which are unjust, unfair, or plain silly, most of them were created to meet a need or solve a problem.

This is very true, but it doesn't represent the views of all libertarians or even all anarcho-capitalists. For a much better approach to anarcho-capitalism—one that focuses primarily on economics and not on morality—check out David Friedman's writings and talks. Here's a basic introduction to his proposal of a polycentric legal system where the market produces all goods and services including law, law enforcement, arbitration (courts), and even national defense: http://www.youtube.com/watch?v=jTYkdEU_B4o. Along with Murray Rothbard's primarily moral/ethical/legal arguments (which seem slightly more prominent, and seem to be the ones you've encountered), Friedman's economic arguments make up the main "branches of anarcho-capitalism."