Humanity itself is trending more toward monoculture socially; I like a lot of things (and hate some) about the cultural trend. But what I like isn't very important, because I might be totally wrong in my likes; if only my likes dominated, the world would be a much less resilient place -- vulnerable to the weaknesses of whatever it is I like.
So, again, I propose for the race as a whole, broad cultural diversity is really critical, and worth protecting. Even if we really hate some of the forms it takes.