Despite his best attempts not to, meesterperfect raises a good point!
How can you decry a girl as "racist" if she won't do black guys yet demand she do black guys for no other apparent reason than their skin color? Fixating on race one way or the other is racism, regardless of the angle or argument IMO.
Also, Neferkauhor's comments seem puzzling to me:
1) You come off as seeming to suggest that no black man can legitimately find white skin appealing, or marry a white woman - it can only be representative of some sort of self-loathing or a reflection of America's racist past/current/future.
2) You also seem to think that anyone being attracted to a porn star is revolting, which is kind of odd as porn works on the basis of being attracted to the women involved. Granted, more than anything you seem hung up on the obviously over-dramatic comment someone made about how attractive they found Gianna Michaels to be (i.e. I think you're taking the comment way too literally/seriously), but still, seems odd to argue that porn stars should not be considered attractive.
Regardless, I think the two best answers have already been raised:
1. Porn viewers (at least the vocal ones) are never satisfied if a girl hasn't done everything possible. Just read a Next Door Nikki or Denise Milani thread to see how many people moan about a girl's not doing for them.
2. Some viewers don't like it because it interferes with their ability to fantasize.