yeah, people do things for different reasons. If there is anything genetic it could be a pretty weak force, easily outweighed by very mild racism or even just wanting to fit in I guess. The shock thing might be a factor for some, as might the "exotic" thing, may have even been a factor for me if I'm brutally honest.
That said, I still think there might be something genetic, who knows?, a taste for exoticism or wanting to shock could be a manifestation of those genes?
That said, I stand by what I said about the smell thing. It's quite common for people (not just racists) to observe how each other smell, try googling "<insert race here> people smell of" if you don't have personal experience. I guess it's natural that we'd all be more immune to the scent of the genetically similar and likely to notice a difference.
I'm completely certain that, for me at least, that difference is very exciting in bed.