From what I can tell as a non-American (so, outsider here), the most opposition to interracial marriages seems to be from a minority of Whites and Latinos (which is saying a lot, considering that a few decades ago that would've been a lot of Whites), a lot of Blacks (especially Black women, who seem to get pissy when a "brother" smashes a White woman), and Asians who were born in foreign countries but migrated to America e.g. the more traditional Chinese, and not their Americanized children.
But I could be totally wrong with my perception because, ya know, Brit.