It seems that diversity is bad for community.
In a recent massive study, Harvard's Robert Putnam (of _Bowling Alone_ fame) found, much to his chagrin, that diversity is a detriment to real community.
The more diverse, the less volunteerism, the less trust, the less social capital. It seems that homogeneity is good for community.
He did find one exception that actually gives me hope, since what I do for a living is about creating community out of diversity. But you'll have read the article at the Wall Street Journal to find out where that place is. Hint: Can anyone say "resurrection?"