Firstly you should watch this http://www.escapistmagazine.com/videos/view/the-big-picture/3183-Skin-Deep Moviebob brings up a lot of good points in the wake of the whole Elba/Heimdall debacle.
Secondly, Regardless on what you think, you'll probably still end up seeing the movie, and if the movie and the actor are good we'll all be back here when they decide to cast Aquaman as a black guy, and people will cite this and Thor of why not casting an actor due to race doesn't matter. And if they're crap, the movie will just fall into cultural nothingness and people won't give a shit. When you really think about it, there isn't much to lose.
Secondly, Regardless on what you think, you'll probably still end up seeing the movie, and if the movie and the actor are good we'll all be back here when they decide to cast Aquaman as a black guy, and people will cite this and Thor of why not casting an actor due to race doesn't matter. And if they're crap, the movie will just fall into cultural nothingness and people won't give a shit. When you really think about it, there isn't much to lose.