There are different kinds of disagreement, I think: my short "will not be on a panel with again" list is based on behavior, not just opinions. For example, it's not that $person1 holds opinions I find problematic, but that she tried bullying me into defending/justifying myself when I asked her not to point a camera flash directly at me. (I don't know her opinions on most things I would expect to be panel topics.) Someone else got on the list for bad behavior during a panel, including but not limited to making it clear that he didn't think anyone my age could possibly belong on the panel in question. (Thinking that would have just been his problem, and saying so to the people running programming would have been iffy: saying so during the panel we were both on was over the top.