I get that. But take a step back and ask yourself how rare it is, comparatively speaking, to have demons opening a portal into the world. Most movies are dealing with shit that would be pretty rare. It's part of the willing suspense of disbelief that we go with it. If you don't have the WSoD, then don't bother watching any TV, seeing any movies, reading any books, or playing any games. You won't enjoy them.
It's just a strange place to draw a line. Yes to demons and proton packs, no to interracial couples. I don't care if you want to hold the line on mixing races, that's your business. I'm just trying to help you enjoy movies more. (Not you specifically, speaking to everyone who is upset by this)
When it happens in a documentary I'll agree it's too far. Otherwise it's just people acting. If it makes you feel better, you can pretend the boy was acting black the same way men acted like women in greek plays.