Let's start with---what do I mean by 'benign diversity'? By this I mean diversity that does not materially raise the crime rate for those it is inflicted on or significantly change the political scene. The archetypical example of this is people of Chinese and Japanese ethnicity living among people of Euro extraction in the US. They've got similar levels of achievement in the things they care about and neither generally aims to use politics as a weapon against the other to any major degree. Furthermore, their crime rates are similarly low, and their interracial crime proclivities are both pretty much nonexistent. So neighborhoods that are mixed primarily between these groups should be just fine right?
Well, if your idea of a neighborhood is one with desolate streets, very little neighbor interaction, and pretty much no kids playing outside (although they do exist in fair numbers, as evidenced by the school bus stop), they're fine indeed. If on the other hand you like a neighborhood with actual community, shared norms, and kids that don't need play dates and the like to actually be..well, kids, they're assuredly not.
Neighborhoods where no group has effective normative hegemony---i.e. the ability to enforce its norms through social pressure---basically aren't neighborhoods at all. I grew up in a neighborhood. I suspect most of my readers did as well. Most of us do not presently live in neighborhoods.
There is a neighborhood of about 95% Koreans centered around a church where a friend of mine lives a few miles from my own. They actually have a community, and they have shared norms. I see kids bikes in lots of people's yards without any locks or the like on them, that have obviously been used recently. This tells me several things. Lots of kids actually play here. They use bikes as a viable means of locomotion. The crime rate is sufficiently suppressed that they need implement no defensive measures like chains and locks. They have a viable community life and probably actually personally know most of the other folks in the community (my friend is one of the very few non-Koreans that live in this neighborhood, but he's a pretty hardcore martial arts geek so he fits in fairly well aparently). On this I wish them well--their community is much like the ones I grew up living in and which I presently only have via my church. This is the way that human beings are happiest living. They're not happy at all when they constantly have to wonder whether the community will back them with respect to things like how many cars its acceptable to park in the street, volume of music playing, how much noise or how late their parties can run, what's acceptable behavior for kids and teens, and a thousand other things. It's nowhere near as bad as the other kind of 'diversity', which I'm well familiar with since I grew up in the South, but it makes for lifeless 'non-neighborhoods'. It also gives rise to the sort of 'grassroots tyranny' that HOAs often become infamous for---in the absence of agreed on norms, administrative and legal rules tend to creep in.