It’s interesting how you can react to the same thing differently at different stages in your life. I was listening to Yom Kippur services a few weeks ago and my reaction was very different from previous times. I heard a lot of 'God is great, God is merciful, God is all knowing, God is all powerful, etc. it occurred to me that this was not about God; it was about the worshipers. If God is perfect in every way then the worshipers are in on the secret. They have a special connection with his perfect God and that makes them special.
Each religion also says that it is the true God and all the others are false gods. So if your God is the true God and if you follow and obey then everything will be perfect, then it’s a small leap to thinking that if you just get rid of all the other people, who worship the false gods, then everything will be perfect. A sure recipe for stoking conflict. From the crusades To anti-Semitism, it’s baked in. And then while you are in the 'we are good, they are bad' mode, it's not a far leap to other tribal feelings of superiority (race, sexual orientation).