When it comes to the mod, does Islam spread itself also? It's another proselytizing religion, and if we're after something realistic it will be more popular than the two-bit religion it is in the game.
Both can be, if the belief is strong enough. But belief alone does not equal religious faith. And your idea of a civic to represent secularism would be best, IMO.Belief!=faith nor religion. I can believe in the existence of aliens, is that religious? I can have faith in humanity, is that a religion?
Christianity didn't spread like that. Most of the spread of Christianity can be attributed to missionaries and monks, not soldiers and prison guards.In reality, the later religions, Christianity and Islam, used bloodshed and things like the Inquisition to make up for their late start.