I'm in a generous mood today, so I'm going to go ahead and assume the principle behind this website is merely another of the seemingly endless stream of increasingly-desperate social networking gimmicks, and not a statement of the belief that relationships only work when they are ethnically pure. Because I guess I can imagine the situation where you have a piece of photo-matching software and want to use it to start a business, and you remember that CSI episode where they said people are attracted to other people who look like them*, and it seems like a really great idea to declare that happy relationships come from people who look alike. And maybe it just never occurs to you to think about what the converse of that statement is: That people who do not look like each other will not be happy in their relationship. And that the world's leading cause of people not looking like each other is being from different ethnic backgrounds. Which is where it starts to get kind of problematic, for me.
On the other hand, if you want to maximize your potential for inbreeding and you don't like any of your cousins, I say go for it.
*It was in the first or second season, I think, the one with the little people.