"Silas" has posted a nice FAQ about objections to anarcho-capitalism on the anti-state forum. I would invite everyone interested in the topic to check it out !
Here is an extract :
Capitalism is as evil as government because it involves hierarchy.
The only way to get around hierarchy is if everybody agrees. (i.e., coercing someone that disagrees into going along with an idea is a hierarchy of its own) If that were the case, there would be no need for any political philosophy, be it ancap, ansoc, conservatism, etc. Political philosophy is the topic of "who gets what" when there's DISAGREEMENT over who gets what.
It's not that humans aren't "built" to agree. It's the fact that the entire field of political philosophy is the topic of what do, given a disagreement. If your theory assumes the possibility of (eventual) complete agreement, it's not a political philosophy at all!
However you answer the more fundamental question of "what should people do when they disagree about how some scarce, apppropriable resource should be used?" you are going to create a hierarchy. If the more needing person should get the resource, that's a hiearchy. If the resource is used however the majority decides, that's a hiearchy.