Horrible situation for the guy, large groups of supporters racially abusing him and absolutely nothing he can do about it. Where else in society is that acceptable?
Problem is a lot of the higher ups in La Liga are part of this "older generation" who think he should shut up and get on with it. That's life. I'd go as far as saying people high up at Real Madrid too but obviously they will publicly side with their guy.
On a side note about him coming to United, where would he play? He's an attacking LW, where Rashford plays and Rashford isn't very good upfront or on the right so has to stay there + neither one should be a bench warmer. Can't see it happening even if he wanted to come.