The reason why marrying outside of your race or ethnicity is bad, is because a lot of times it causes cultural problems. If you, love almost everything in your culture and how it is and what it's made up of, you are going to have a hard time being with someone of another ethnicity than you if they feel the same way about their culture. A lot of couples say that they will compromise their traditions, but down the line you are bound to hear things like, "Well, this is how we do things in my family" and that's when the drama begins. Different foods, dances, language, etc. A lot of times it's a lot of work to have interracial marriages work. I guess it can work when both people don't have any traditions and want to create their own.
P.S. Sorry if I repeated anything that was already said in this thread. I didn't read all the comments. lol.