extreme beliefs that may lead to unreasonable or violent behaviour

religious fanaticism 宗教狂热

Fanaticism has already destroyed countless lives. 狂热已经摧毁了无数人的生命。

extreme interest in something, to a degree that some people find unreasonable

the fanaticism of football fans 足球迷的狂热

His fitness fanaticism sets him apart from his friends. 他对健身的狂热使他与他的朋友们很不相同。