They made nazism illegal, Islam is also a Totalitarian Ideology responsible for the death of millions.

The only difference between National Socialism and Islam is that one was thoroughly defeated and we learnt to never let it rise again.

It is also the case with communism, communism is the rejection of humanity and is the most totalitarian and deadly ideology of the three, but we didn't defeat it like National Socialism so it is not illegal (in Europe) and heavily stigmatized.