The same argument can be used against Christianity - trying to wipe away the stain of sin is absurd, since sin is literally the disease of human nature.

An ideal is not invalid because its difficult - being difficult is what makes it worthy of being an ideal.

Besides, anarchism has already been figured out, and sporadically implemented. The American Constitution is an example of anarchism in the real world. Should we abandon it completely, now that oligarchs control the government?