All of this seems pretty true to me. There were even studies that showed pretty clearly that ethnically homogenous communities were happier than ethnically mixed ones.

There are lots of good reasons not to actually exclude different people from a society. Immigration's been shown to be a net good for most people involved, and of course uprooting people from a society they've grown accustomed to is harmful. But these only counterbalance the above claim, not disprove it.

I think it's pretty self-evident that anything that brings nudists together with those Arabs who freak out if every inch of a woman isn't covered by a burka is going to be a net loss for both groups.