It's like what mistea said- that question may force some people to acknowledge their own stereotypical thinking. This may not necessarily be a bad thing, but to do it here and in the open might incite some hard feelings.
I can't speak for anybody else, but I think many of us here simply want to expand our options and open our minds further. For most of us- to say "I'll only date within my own race" not only narrows down our choices, but is also another form of prejudice.
At the risk of invoking a cliche, most of us here know better than most that "love knows no color".
You may not realize this, but your question is potentially incendiary. That is, you are inviting the acknowledgement of all sorts of stereotypes (either positive or negative) which is never a good thing.
Perhaps this is a bit naive, but I would hope that while everyone has their physical preferences, most people are not adverse to dating within their ethnicity.