It’s not against dark humor. It’s against what you identified: people hiding behind it or qualifying their bigotry as dark humor when they’re really just assholes.

My humor is dark af and I take no offense because this isn’t about that.

Edgy humor has a butt to the joke, and/or the joke is made due to someone’s misfortune, at their expense. It’s inherently problematic in the sense that there’s a risk of offense to those who have been victims of similar misfortune. The solution, of course, is to be funny enough that the humor overpowers the offense and/or doesn’t focus the humor on being mean to the victims

Dark humor itself isn’t the issue, however a majority of the people who claim they have “dark humor” are actually just massive bigots who don’t want to be called out so they mask their hate as thinly-veiled “jokes”