Well, again, I'm not an expert. But, I've read some stuff and watch the History and Discovery channels religiously (And they're always right. ::Sure). So, what I've heard/read is that there is a THEORY that one reason humans go to war is biological imperative. It used to be one of the few ways to increase the size of the gene pool. Now, of course, there's more moving to different countries and social mixing of different ethnicities and we don't need war to widen the gene pool, just some airplane tickets. So, biologically, interbreeding is a good thing and will lead to humans not going extinct as soon as we might if we just bred with 'our own kind.'*
*Ethnically, that is.