I think the opposite way. You are infering that unless there is a specific reason to justify it, that diversity should not exist. Why cant there be diversity for diversities sake? I dont agree with diversity being a important part of game, but do I take note of cool enthic characters? Yes I do. Speaking of ethic characters, isn't it strange that Japan is responsible for all the coolest black characters? Thats a damn shame.
Perhaps I was not clear and this is a very complex topic for me but I was not at all trying to infer that there needs to be a specific reason for diversity, or otherwise it should not exist. And maybe our way of thinking about this is not even that different.
Maybe I get it out better this time: A cast that reflects the reality of the setting and context is vital (like a game about apartheit in South Africa with only asians would be broken in my regard). Or a game about the struggle of transsexuals without a trans-person. That would be just silly.
Other than that, diversity is of no importance to me. Thinking that less diversity makes something better, to me, is not okay (like: "I wish there were less asians/homosexuals/etc. in it"). BUT thinking that more diversity makes something better, to me, is just as bad (like: "I wish there were more asians/homosexuals/etc. in it").
It is easy to see, how wanting less diversity is often a bigger problem, since those regards typically (but not always) came from racist individuals.
But wanting more, to me, as I said, is just as much of a problem on an individual basis. Let's be polemic here, just to illustrate a point. In "Family Matters", or "The Cosby Show" the cast was all black. "It would have been better if there were more white character" - to me, that is a racist statement. "Married... with children" was all white. "It would have been better with more black characters" - to me, that is a racist statement. Just as much as to say: "it was so good because it was all white."
Or in another way: diversity has nothing to do with the quality of your product, it is absolutely neutral, unless the setting and context of your product requires a specific set of people.