I would say this is a big reason to not believe in gods. True believers would claim that the other side did not have the true religion. Very strange this "true religion" stuff. Pentecostals think they would still be Pentecostal even in Iran. I'm sure a lot of Baptists think the same. A lot of these believers think their god stacked the deck by allowing them to be born in the right country. It is a strange idiocy.
Ever priest/imam/ witch doctor in the world is in competition with every other. And when the only two products you have to sell, is a belief in that your followers have an exclusive access to truth and gods gifts, plus absolutes and the idea of perfection, then detail matters to an extreme. It is no good saying. "Yep god is going to let them into heaven as well." Because then you have nothing to sell.
Talking of heaven...
Understanding how the biblical prophesy is fulfilled. As written, Abraham says to Ishmael he will always be in hostility towards his brothers. Ishmael patriarch to Islam always in hostility to brothers of Judaism and christianity.
He will be a wild donkey of a man; his hand will be against everyone and everyone’s hand against him, and he will live in hostility toward all his brothers.” Genesis 16:12