So I think it is totally fine for a group to ban particular controversial topics during meetings. What I think causes the problems I am worried about is banning people who have known controversial opinions that are expressed elsewhere.
If a specific person is unwilling to refrain from talking about their favorite subject at the meeting, I am then fine with banning them for that specific behavior (so long as it is done with a reasonable process, involving warnings and requiring people expressing the opposite point of view to also not start the arguments)
So I think it is totally fine for a group to ban particular controversial topics during meetings. What I think causes the problems I am worried about is banning people who have known controversial opinions that are expressed elsewhere.
If a specific person is unwilling to refrain from talking about their favorite subject at the meeting, I am then fine with banning them for that specific behavior (so long as it is done with a reasonable process, involving warnings and requiring people expressing the opposite point of view to also not start the arguments)