There is also a modern definition of fascism as “Inequality through mythological and essentialized identity”. Basically you foster belief that because of some mythos you are special (gender, ethnicity, religion), and that allows you to deserve more or discriminate against the others. Religions that demand blind faith are contradict modern science more or less have to foster part of this thinking. Not that you need religion for this but it's close. And not all extremism is fascist ofc.