because it could lead to thinking that it's just a preference not to be attracted to trans people, or to POC, or to any marginalized group.
Because it is.
Despite the fact that I have never met a (non-asexual) white person who wasn't attracted to at least
some non-whites, attractiveness is still an utterly subjective and personal experience. You don't
ever get to tell a person whom they have to find attractive. It's simply not your business. And even if it
was, it wouldn't matter because we don't really get to consciously decide who is and who isn't attractive for us.
Try to change the overall
cultural understanding and representation of beauty, if you want to, that's a noble goal, but don't make this personal. It just makes you seem like an authoritarian asshole.