@TMW - you realize the two are *not* mutually exclusive, right? Lookup anarcho-communism. The problem with anrchy as a theory and anarcho-anything in reality is that anarchy assumes "common sense will prevail" but "common sense" doesn't mean the protection of the weak. Man is an animal and, as such, will do that which gets him the biggest reward. We subconciously want what the Joneses have and want to be better than everyone else. If we didn't have laws and the law didn't have teeth, we would devolve into chaos like something out of a post-apocalyptic movie, and the moment you have laws and give the law-enforcement body teeth, you have a government. A very limited one, maybe, but a government nonetheless, and you cease having anarchy. Anarchy, by it's very definition, is lawlessness because laws imply a governing power to enforce and punish their violation.
And when you talk anarcho-whatever, the whatever part is a form of government which invalidates the anarchy part of it and eventually comes to a state of either complete chaos or becomes the second part (capitalism, communism, whatever). anarchy as a governmental form is insustainable because it will either fall into chaos if enough of the group puts self above others, or will convert to some form of government when the more socially responsible individuals bring about some form of law and order.