All of these responses have been good ones, and thoughtful ones, but I wanted to address something specific in the OP. There was mention of people who only marry within their own race because they believe in the propagation of said race.
My grandmother was a black woman who grew up in the deep south and had fairly strong feelings about the mixing of races, despite (or perhaps, because of) the fact that her brother had married a white woman. She felt that we might eventually lose our identity as a people.
Personally, I have mixed (sorry!) feelings about an attitude like this. When you’re talking about a people who have historically struggled a great deal, you can understand why there might be some fear of losing an identity. But I also think it smacks of separatism. To me, it is like saying, “This past misery is ours, and no one else sould have a right to claim any part of it.” Wouldn’t all people benefit by the sharing of culture and history in all manners, including interracial mixing? The problem, in my eyes, is that people who hold such a view think that interracial mixing is a subtraction of, rather than an addition to, their own culture.
I will never forget talking with a close friend of mine who is Jewish during our late teen years. I was teasing her about the fact that she’d never dated me. Now, one side of her family is quite wealthy, and she told me that there was once a young black man that she had been interested in, but that when her grandparents found out, she was told in no uncertain terms that she would lose any inheritance and be disowned from the family should she ever go “that route.” Now, I’ve met her family, and they’re all very nice, friendly people. None of them have ever had a problem with me. But apparently, that’s because they’ve never seen me as a threat to their bloodline.
Is it racist? I think maybe that’s too harsh a term to assign to it. But I think it is definitely a stepping stone in that direction. I’m hopeful that this sort of attitude wanes as new generations step onto the scene. I think it is tragic to suggest that you should not love another human being because their culture might somehow taint your own. Even if the intention is not to promote an attitude of superiority, it certainly devalues the merits of the other race(s) involved and any potential union of the two.
I apologize for the ramble – those are my $0.02, sans any conclusion, for all to pick apart.