The very construct of the concept of a religion leaves the potential for extremism within itself.
Let me explain why I think this:
- Religious beliefs are based on believing in an unknown or unexplainable higher power.
- The core thesis and different concepts of a religion are communicated through scriptures or mythology, or both.
- In most cases, these source material were produced for a significantly different cultural and historical context. Also, they are mostly vague about their concepts and leave a lot of room for interpretation.
- Most religions do not encourage, or are not very welcoming of critical questioning of such concepts and their core thesis.
- A significantly very large proportion of the believers of religions do not have any in-depth understanding of those source materials (2).
- Because of the vagueness in source materials (3), there is ample opportunity for widely varying interpretations, and some of them would inevitably be extreme in the context of current societal norms.
- When such extreme interpretations are presented to believers, they are less likely to question those or even cast any doubt, because of it is not the norm to question (4).
- In such situations, believers are also bound to believe them because of their lack of understanding of their own religion (5).
- In isolated and mono-cultural societies, this can go on for long without being questioned or challenged.
- Even if they are questioned or challenged, those arguments can always be countered by the core tenant of a belief (1), and such extreme beliefs can further get strengthened as a way of self-preservation at perceived persecution.
These are my thoughts as a non-believer. I may be totally off track, but at least this explains things for me. If there is any better explanation from believers, I am always open to listening.