I like the idea of different religions living harmoniously together, but this only actually works for defanged religions. Religions with teeth that try to occupy the same space are gonna eat each other alive.
Honest question, why do you think different Christian denominations lived relatively well together in the US? Was it because they were fundamentally the same religion?
Just speaking for myself, but I grew up Calvinist, and we had a set of core doctrines that, if people adhered to, they counted as 'one of us' - even if they weren't Calvinist. This encompassed nearly all protestant Christianity, and we heard sermons about getting along with them.