The noun fanaticism is an extreme interest in something that non-fanatic people find unreasonable. Sometimes fanaticism leads to violent behaviour as well as extreme stalking (especially celebrities).

Synonyms are extremism, zealotry, bigotry, or militancy.

The word origins from the Latin adverb fānāticē meaning “enthusiastic, ecstatic, raging, fanatical, furious”. Its first recorded use was in 1652.

Fanaticism is not healthy especially for young people.

All she does is fanaticism over her western idols.

There’s nothing wrong with being religious but religious fanaticism is a bit too much, right?