It’s a pattern I’m seeing too often in fandom: Someone has supposedly done something horrible, so this person shouldn’t be a convention guest, be on the program, whatever. Details are scant. If you ask, you might be pointed at some large corpus of work in which the person in question has said horrible things. Somewhere in it.
How are you supposed to decide if it’s true? Well, really, you aren’t. Your friends are saying so, and you’re supposed to agree with them. It amounts to a campaign by innuendo. If you question it, you may be a questionable person yourself.
The accusers may just not want to give their target free publicity, but they have to make a choice. A lot of times the right thing is to keep the dispute private, but if you make claims, you have to back them up. They might be concerned that the person they’re accusing said hurtful things, and they don’t want to subject more people to them, but they need to choose. It’s often better just to deny a jerk publicity, but an accusation without details is an injustice. It doesn’t give the one you’re accusing any chance to make a defense, and it doesn’t let your audience make a decision for themselves.
That sort of accusation can also be a power play. The technique of discrediting an enemy with bogus accusations has been around forever. The threat of doing it can be a tool for bringing people in line. One person in fandom tried it with me; it didn’t get my cooperation, and if she ever tried to carry it out, it was so complete a flop I never noticed. It did make me more wary about believing rumors, though.
If you have a complaint about somebody and want me to take it seriously, provide details. It’s not my job to do the research on your accusations.