Well, it's not diversity for the sake of diversity, it's diversity for the sake of humanity. More precisely, depicting a diverse humanity would be, I believe and expect, for establishing part of the setting, so that the drama occurs with respect to the diverse species that is humanity. Not all aspects of the diverse humanity need to specifically be a focal point for drama.
However, perhaps somewhat paradoxically, the lack of drama, with respect to certain of these myriad diversities that people today find objectionable, would itself be a kind of story point. Wouldn't it? It would be saying that people in the 23rd century don't find these things objectionable, again to establish that aspect of the setting.
As others have basically said already, that setting is implicitly hopeful. Humanity is not like the Borg. We accept differences among ourselves.
I didn't see your post until after editing mine. To be honest, if you really want to get all science fictiony and futurist about it, the races will have had another 200 years to commingle and this shouldn't even be a point. In fact, we'll probably be MORE like the Borg than humanity anyway given the current cell phone proliferation. Besides, we're not actually talking about the future, we're talking about the Star Trek Universe which is (already) different from it's own canon. LOL
Don't take my point wrong, I'm not arguing against Diversity, Diversity is good, it's shows us different paths and expands our tiny little brains which is always a good thing. But I find the whole debate about diversity unsettling, as if we want the future to look exactly the same as today just with better toys. That isn't going to happen.