Things that offend me: racist stereotypes.
Things that don't offend me: white people playing white people.
Of all the things to be mad about, this ain't it.
#MU*sSoWhite is a nonsense hashtag. I assume it's referencing #OscarsSoWhite. These are not morally equivalent crimes.
The Oscars (and RL media in general) being white-dominated is a problem because non-white people don't have the same opportunities in life, nor do they receive the same/fair recognition as their white counterparts. Real people are affected when out of a diverse line-up auditioning for a role, only the white actors stand a chance, or white people are paid more, etc. And when non-white children grow up only seeing white protagonists in the media they consume, they're made to feel like they don't matter and never will have the same opportunities white people do. Similarly, when media depictions of women give the impression their sole purpose in life is to be a romantic/sexual satellite for men, that gives people of all genders the wrong idea of how to treat women -- and in women's case, how they ought to treat themselves.
No one is hurt when white MUers play white characters. You aren't paying your played-by royalties. You aren't denying starving black artists the opportunity to perform in your world. You aren't taking away representation from POC. You are representing yourself. Everyone who plays these games has the opportunity to represent themselves and live whatever gay/female/black/disabled/whatever fantasy they like. We make our own superheroes.
I have literally never looked at a mostly white, mostly male or mostly straight ensemble on a MU* and felt ostracised by that fact alone. It would be different if, out of 10 female characters and 20 male characters, all 5 leadership positions were filled by dudes. It would be different if someone called my gay/POC character a slur.
I have however frequently been disgusted by POC characters clearly played by someone who doesn't belong to that minority group, who uses the character's "exotic" skintone to base the entire concept on. For example, a weed-smoking, uneducated black criminal who spends most of his time talking about KFC, drugs, and white booty. (Yes I have run into this. MULTIPLE TIMES.) Please don't encourage these people by suggesting they're heroes for providing #representation.
What I do think played-by choices often reveal is beauty standards. Most people pick faces they think are attractive. I often cringe when I read descriptions that wax poetic about how super blonde and teutonic and alabaster-skinned some elegant specimen of Western masculinity is, or when people list their "race" on a character page as Nordic/Irish/white, especially when that's a custom field rather than a default one. Maybe if you're one of these people it's worth examining your own biases.
Do it quietly, in your head.
And direct your white guilt towards more important causes.