Is anarcho-capitalism utopian?

No. Anarcho-capitalists tend to be pragmatic, and argue that, no matter how good or bad man is, he is better off in liberty. If men are good, then they need no rulers. If men are bad, then governments of men, composed of men, will also be bad — and probably worse, due to the State’s amplification of coercive power. Most anarcho-capitalists think that some men are okay and some aren’t; and there will always be some crime. We are not expecting any major change in human nature in that regard. Since utopianism by definition requires a change in human nature, anarcho-capitalism is not utopian.