If you mean by "the opposite" that everybody believes the same thing, then theoretically yes. However, that is very unlikely and I assume there will always be people with different views/opinions.
The more you put people into "separate boxes", the more you segregate them. And I agree with the previous reply that religion is one of those things that puts you in a specific box.
I think they mean that people in large groups segregate themselves into smaller ones, by whatever characteristics available. If they had the same religion they’d be separated into orthodox and progressive versions of it, or people who had come off well out of the last great flood vs people who got screwed by it. And then they’d create a religion as explanation for the flood and why it was from god/the devil.
