This is a really interesting post, Sam. Funnily enough, I recently have been exploring anarcho-capitalism, and trying to figure out what I make of it.
The concept appeals to me in many ways. Also, I think its proponents do believe in the goodness of humankind.
However, I don't know if any philosophy can stand up under all circumstances.
It's difficult to assess hypothetical situations. But, just as an example, I've wondered how thoroughly an anarcho-capitalist could have stuck to his or her views in Germany, just before the Second World War.
RE: Political Theories on Human Nature