Definitely 100% I think it's good not to assume what people are. I guess I just felt like "well of course this person is (x) if they're playing like this". But I guess I just never really challenged that assumption with any alternatives.
For virtually my entire internet existence, if I don't say anything to the contrary, people will 100% assume and I and everyone else on the internet is white. It's a part of what explicitly keeps me from trying to explore certain things as a black character that ironically white people might find problematic if they don't contextually understand what I'm trying to do.
Something like this might be like the movie Attack the Block, where John Boyega and his friends are delinquents from the projects starting trouble and such. But the point of the movie is to subvert that they're ultimately kids who are the product of their environment, and when presented with the opportunity to do good and be more than that, they will.
Obviously it might be a simplistic interpretation on my part, but I think a narrative like that is hard to do in a MUSH in the sense that it requires you to dive somewhat into problematic trope in order to build to the positive aspect, and OOCly it just feels like there's always that hump of, like, this is a white environment where I have to be very careful about going too deep lore black or they'll think I'm being problematic, am secretly a white person, or any other number of things that keep me from fully expressing myself.
Of course it could all be all in my head, but people definitely 100% assume that everyone else is white usually. So these just feel like things I have to take into consideration. And I can't always depend on the idea that people will understand or even believe my intent, which I think is something that every MUSHer has experience with.