This question is separating one and the other - both are bad - but I think religious extremism is powered by extreme greed causing extreme poverty and vulnerability.

So actually, maybe I do have the answer. Get rid of extreme greed, and religion does not go extreme.

Even the crackpots calling for genocide won’t get a voice.

Correct me if I’m wrong but even Hitler employed the tactic of blaming the Jews for the poverty (and other things) in Germany. But in reality it was the Great Depression. Germany was one of three nations that had the highest unemployment in the (western) world.

Yes, Nazism wasn’t a religion but a cult. But religions can involve a god, many gods, or idolise an object or a person. Hitler was it. He was like a war god.