There may be some 'true believers' in positions of political power. But far more frequently, I suggest it's a matter of using fanatics and fanaticism when it's convenient, and dropping it when that's convenient.

A readiness to do battle or repress 'the others' , outside or inside a society, involves a decision as to who are 'the others', and who are 'our kind', but religion is only one of the markers used. "Race' or colour or age or sex or class can do just as well. Sometimes just what football team people support, or how they choose to dress. Or what kind of music they like.