I’ve run lots of library board meetings and the Hitler comment is not what would have crossed the line. Rather, speaking out of turn would have been.
The public can speak (and I’ll let them say whatever screwed up shit they want to say), but each person gets their turn, and each person gets a time limit (I think ours is five minutes). After that, the only people that get to speak AGAIN are the ones that are directly addressed a question (usually by a board member, though it could be a subsequent private citizen).
But if you start screaming anything to disrupt the running of my meeting (that I get paid in cookies to run!), I’ll give you a warning, then boot your carcass out of my meeting room!