Fascinating and thought-provoking. It's certainly not just religion, but any deeply-embedded beliefs that can provoke anger and even violence. Some people treat politics like a religion, and even if they mean well, even the slightest challenge to those beliefs can provoke a violent reaction.
A few years ago I did a lot of study into the history of the Pacific Islands. One thing that interested me is that the first Europeans to travel to the Pacific islands found large differences in various island groups that were very remote from each other. Some communities did seem to be very peaceful, while others were quite warlike. The Fijians were actually excellent surgeons, because they fought so many wars that they'd learned how to patch up wounded people!
I personally doubt that these peaceful or warlike tendencies are in people's DNA - it's because societies go through changes and variations, and the Europeans probably encountered the Fijians when they were in the midst of lots of power struggles, while the Marquesans were going through a period of stability. And certainly the Fijians (and the Tongans) had very complex social structures and complex beliefs. It's a fascinating subject.