In my experience anarchists tend to suffer from a mix of idealism and naivety. The general premise most anarchists seem to believe is that the state is responsible for all the problems in society, and if it was somehow abolished then people would just naturally act in cooperative and enlightened way. This appears to be premised on the assumption that most people think the way anarchists do.

There is an important question that anarchists need to answer that they either ignore or hand wave away. First one being why centralized and hierarchical structures keep arising in human societies time and again. After all, humanity started in what are effectively anarchist societies when we lived in small tribes. So, why is it that we see centralization inevitably appear, and why don't we see any successful large scale societies in existence based on the ideals of anarchism.

The answer is of course that there are selection pressures that favor centralization. On Authority from Engels explains these pressures very eloquently. So, we see societies that embrace centralization end up outcompeting those that do not.