The plot for this movie seems crazy as hell but I'm all for Stockard Channing to have a nice role again. I don't know what to do about Michael Jackson because either way is, quite frankly, rather disrespectful without any malicious intent.
For they chose a black actor it would be bizzare, but I wouldn't say disrespectful.
Regardless, I do think choosing a white person to play MJ is a sound choice, he didn't look black or white or any other ethnicity at the time, that's true, but at the very least there could be some resemblence in skin tone.
What will never be known though is whether him starting skin bleaching caused the vitiligo. (Which is entirely possible) either way his stark white appearance would not have been fully caused by it as it is a desease that only produce patches. Thus he bleached/used makeup to match lighter colour.
Vitiligo was the main cause of bleaching in this case, the reason why the skin appeared to be 'evened out' is because he resorted to use make up and bleaching products to help. At least that's what I understand, MJ always identified himself as a black person anyway, even when he was whiter than white people.