I don't buy that. All those whites who had a problem with it know that Norse mythology is just that. A myth. Not to mention the vast majority of those whites aren't Greek to begin with. A bunch of Greek gods living in an alternate dimension with super powers is perfectly fine entertainment, but if ONE of those Gods is Black, suddenly that's too much of a stretch for their imagination. And lastly the typical response they have for minorities (especially Asians) who complain about minority characters constantly being replaced or portrayed by white people in Hollywood is "It's not real anyway, stop complaining", "Use your imagination", whining about the race card or something along those lines. But you have movies like Thor or Hunger Games (which from what I've read the Black characters in the movie are actually described as Black in the book) where whites turn around and complain about Black actors portraying characters they feel should have been white. But when it's reversed, they don't see a problem and they sure as hell don't see why anyone else should . And I'm going to start adding disclaimers to some of my comments that this isn't ALL white people but it's a large segment.
True, but many myths also include people who are half-horse or of another people (dwarves, inhuman frost giants, green sprites, pixies, etc), and when's the last time you saw a half-equine Greek dude? The gods of death and the underworld are portrayed as black (the color, not the race) in many myths. So can a black actor play that role, or a white actor painted black? I think there are certain people for whom it's explicit. Thor, for example is explicitly referred to in mythology as Nordic. His full name is Thor Odinson, is universally held to be blond and is meant to be the ideal of Norse manhood. However, Heimdall is just a dude who guards the Bifrost. No genealogy is explicit. I agree it's kind of weird and unexpected, but not a deal-breaker necesssarily. At least for me.
A few people seem to be missing a very vital point about Marvel's Thor. In the Marvel universe he is NOT actually a Norse god but rather a demi-god from Asgard. His Norse god mythology comes from the fact that Asgardians just so happened to come into contact with Vikings and due to their very advanced technology the vikings perceived them to be deities. This is explained in the film at least twice. :smt021