What is the explanation for the phenomenon of extremism in religion?

Excessiveness, extremism, and rigidity in religion, as well as negligence, leniency, moral decay, and dissolution—both stem from ignorance of the Sharia (definition). The methodology of Islam is moderation, and what is required of Muslims is uprightness without extremism or negligence. For a comprehensive explanation of the phenomenon of extremism regarding its causes, effects, and cure, one can refer to Dr. Abd al-Rahman ibn Mu'alla al-Luwayhiq's books: "Religious Extremism in Contemporary Muslim Life" and "The Problem of Religious Extremism in the Modern Era: Causes, Effects, Cure."