I dunno. I found the Stalin angle to be far more offensive than anything else. Imagine if they did a similar thing where people dressed up like SS officers and one was designated Hitler?
(If you don't believe this, pay attention to pro-Palestine protests on college campuses.)
Why is it worse for a light skinned woman to play a darker-skinned woman than for a white man to play a black man?
And it's worse because of the history of black face and why it was used
Tropic Thunder got away with blackface for the same reason Saturday Night Live gets away with offensive jokes. It's satire, and they're mocking the offensive acts.