The basic moral foundation of most anarchist philosophy is universal. States do nasty things such as wars, theft, murder, violence, torture, jailing, spying, destruction, etc. If you apply a universal moral standard these things are still considered wrong, even if an organization called a 'state' is doing it. Even if many people believe it's ok for this organization to do it. It doesn't matter when a moral standard is universal.

A good way to think of anarchists are pacifists. Pacifists think all violence is universally wrong. Most people are not pacifists although and feel like violence is OK in some instances. Many of these non-pacifists would also agree in an ideal world that pacifism is what humanity should follow. But they recognize they don't live in an ideal world and thus are not pacifists.

Anarchists are really the political equivalent of pacifists. No force or coercion is ever acceptable in any circumstance is the basic foundation of anarchism, everything must be voluntary.

So according to that political philosophy taxation is still theft or extortion, just like self defense is still violence and soldiers killing in war is still murder to a pacifist.