In the book The Socialist Tradition, Alexander Gray states (pg 3):
An anarchist society is conceivable only if all concerned are the embodiment of reason and restraint. Not merely therefore should an anarchist be a man of reason; he should also combine with his own reason a wholly unreasonable belief that all others are equally reasonable.
I would agree with this quote in the context of an anarchism that expects certain values, like abstract concepts of justice or equality, to be universally held. However, as a free-market anarchist I suggest that a society in which people hold many different values is possible, just as we live in a society in which Fords, Chevrolets and Toyotas, among others, address the values of a wide spectrum of car buyers. See my blog entry, "Competition as a Discovery Procedure or Ethics" for thoughts on that subject.