bathroom issue is full of stuff, if you have a richard go into the guys bathroom
if you have a vagerdazzler 9000 go into the womens bathroom
simple as that
except that can reveal trans people who were otherwise passing, causing others to single them out for harassment. if you're being a remotely decent person, you're not looking at anyone else's privates in the bathroom anyway, so it doesn't matter there either. if anything, a gay in the bathroom is more threatening.
i mean, the people who fear-monger about "but creepy old men will pretend to be trans to molest ur wife/daughter!" probably would complain about gays using the same bathroom as them, too, if only they had an easy way to tell. in practice this risk is negligible because the ones who aren't even TRYING to pass are pretty obviously up to something anyway.