"One thing that does strike me is WHY it is seen as wrong for someone white to "black up" for a role."
Interesting difference between film and theatre -- in the theatre, we are (nowadays at least?) fine with a black King Lear. We now have staging of opera and Otello where the lead character has to convey that he is a Moor through some means other than blacking up.
And we now also have had female Hamlets (other than the traditional we're at an all girls school, so most of us will have to play male roles. Time to don the cod-pieces girls! Said of course with a Maggie Smith Jean Brodie accent........).But different in film? In film we expect 'realism', but then we end up with black actors reduced to first drug dealer/second drug dealer/first whore/second whore etc..........
So, are we saying that actors ARE actors, we know they are not a scotttish king, or a prince of Denmark who's a bit miserable, it's their job to convey that character without just a simplistic wear the clothes and make-up so you look right. If a white performer is playing Otello, then blacking-up is wrong...............
Again, we come to the fact my extremely strongly held view that femininity is a performance that anyone can potentially do, but that femaleness isn't. That in some cases(?) a female actor can have as good an interpretation of Hamlet, say, as a male actor, and perhaps even better? Because the theatre is one more step from reality/realism than film, because you have documentary films but not documentary theatre (apart from real life, and there are always some people whose real-life performances are terribly addictive!).
Performing femininity isn't the same to me as a male performing a female role, either on the stage or trying to do so in real-life. I think we can make a very strong case BTW for female actors being 'allowed' to perform as many male roles as they want (because the 'great' roles are mostly for men, so why should women not have a chance!). I think if a male tried to play a female role on stage by (just) performing femininity and not much else, it would not convince. And frankly, I have come across exactly that where a M2T actor was playing a female role, but it just came across to me as a camp gay man which had me wondering why this character was a camp gay man...........