Given the context of them being aliens there isn't much of a problem with one of them being black. However, let's be realistic, it probably does have
some overtones of social commentary. Why would it be alright for people to complain about white actors playing traditionally non-white historical/mythological figures while it's okay for the reverse to happen? Two wrongs don't make a right. A better answer would be to develop movies based upon mythological figures from other cultures than to try to make one culture's mythology multicultural. That's just absurd.
But like I said, within the comic/film's context it makes sense.
Logan Westbrook said:
Although Elba doesn't look like a typical viking, it's not as if he's playing a historical figure, and it's hardly the only liberty that Marvel has taken with the Norse pantheon. As insults go, saying that the Norse gods were actually aliens with some really advanced technology - which is actually true in the Marvel canon - would seem to be much worse than casting a black actor as Heimdall, but strangely, no one seems to be bothered about that fact.
I like Norse mythology, and I have to say, I am far more upset with other things than the black Heimdall. The point at which I laugh hysterically whilst viewing the previews is when Odin (Anthony Hopkins) makes Thor swear to uphold the peace...
WHAT. THE. FUCK!?!?!?!
It's one thing to take some liberties with characters and minor facts, but this simply
isn't Norse mythology
even in its most basic spirit. Norse mythology revolves around war. The universe begins in war and it ends in war. Not only that, but war is essentially the meaning of existence. It is not just a sad fact of reality, but something glorious. One only gains entrance to Valhalla by dying in battle. Cowards go to hell. Death in battle was the goal, and most Norsemen feared what they called a 'straw death' (i.e. the peaceful death that everyone seems to value in modern society). Old men would often go out into the roads with their swords and chain themselves to some of their treasure so that passers by would attack and hopefully kill them.
To suggest that the goal of the Aesir is to uphold peace flies in the face of everything that is central to Norse mythology. It's one thing to criticize their value system, but to misappropriate it in this way is just blatantly disrespectful and a sign of callous arrogance and assumed cultural superiority, if not simply a sign of downright willful ignorance.