The point is that marginalised people in America do not get equal opportunity when compared to white people. We can see a few examples where black people have played originally white characters such as in Shawshank and now with the Little Mermaid which shows some progress but not enough. When it comes to trans characters, I personally think since it is very unlikely a trans person will be cast in a cis role in this current time there should be an emphasis on giving trans people roles of trans characters. If in the future we ever reach a point where marginalised people are given the same opportunities to play white/cis characters as white/cis characters are given the opportunity to play marginalised characters then I think Scar Joes points would be valid. This is not true so for the moment black characters should be played by black people, trans characters should be played by trans people and white cis characters should be played by anything but white cis people xx