Both Americans and Britain have been complaining of police racism for years, as have there been discussions on both sides of the pond of racism in the judiciary and every other power structure. The justification can be found in all those links I've given that you seem to have ignored. The discussion in the Trayvon case is only an extension of a much larger conversation that many people have been having but the mainstream have mostly been ignoring.
Personally, having seen Zimmerman supporters on Twitter today, I'm not sure why anyone would want to include themselves in that group. It's been vile.
Also, saying that you're willing to sleep with a black man makes you not racist is like men saying they're not misogynistic if they sleep with women. It's doesn't make much sense.