Usually, and that is certainly what the moderator should do. But sometimes they don't. Sometimes they go off on their own tangents. And if they do that, it is perfectly acceptable after a while to say (while looking innocent and hopeful), "Can the rest of us introduce ourselves?"
I was on a panel several years ago where the moderator clearly didn't want to let the rest of us speak. He was an expert on the subject matter, but if he didn't want to let other people have a chance to share their ideas then he should have asked to do a solo presentation. Or not volunteered for panels. The moderator is there to facilitate the discussion, not to dominate it. Don't ever let yourself be bullied into silence.
Years before that a friend and I were on a panel with the guest-of-honor, a very popular author, and there is no doubt that most of the audience was there for the sole purpose of listening to him speak. That he did speak more than the rest of us that was fine and as it should be, but he didn't have to be so condescending just about every time he opened his mouth. And he said one thing that made my friend furious ... and I think speechless, since she didn't respond at the time, and she's not at all shy. He said that all authors were arrogant rapists. What a thing to say when two or three of the other panelists were female!
If someone says something to offend you or that you strongly disagree with, speak up. Don't be offensive in return, or combative, but don't be shy about politely challenging them. Panels where everyone just sits there and smugly agrees with everything the others say are generally boring, and almost invariably short. Audience members who came hoping to hear a full hour of discussion will feel cheated if it's only half-an-hour because no one seems to be really engaged with the topic. They appreciate a lively discussion. (In fact, they enjoy something that verges on a brawl, but you don't want to go that far.)
I hope it doesn't look like I am dominating the discussion, but here's another example from my own experiences. I was on a panel that had something to do with divination or magic, I forget which. Maybe both. One of the other panelists didn't show up. I think that person's presence was supposed to make for a more balanced discussion, but they weren't there, so it was me and the Bay Area Skeptics (or as I like to think of them, the Bay Area Skeksis). All three of them were men and I am sure they expected me to be an air-headed New Age hippy-dippy female and that they could crush me with their masculine logic. Two of them were rude and condescending, but the other was polite (and a little dazed that he was facing a wholesome suburban housewife who was perfectly articulate, even if she did read Tarot cards and crystal balls, instead of the kind of person he expected, someone with a strong aroma of incense and marijuana, speaking New Age cant.)
It was three to one and they obviously expected most of the audience to be with them. Almost certainly all but a handful of people were on their side when they went into the room. Which made me think I had a ghastly hour ahead. But I get stubborn (as many of you know) so I refused to be intimidated and I stood up for my own opinions and experiences.
But here was the marvelous part. The two Skeksis who were loud and obnoxious became even more so as the hour went on, and the more they blustered, the more sweet and reasonable I was. Which completely won over the audience. After the panel was over, people were coming up to me, shaking my hand, telling me how much they enjoyed hearing me speak. It was possibly my moment of greatest celebrity. And I know it never would have been that way if those two men hadn't been complete and utter jerks.
So if you do end up on a panel with someone who is truly obnoxious, think of it as an opportunity.
hopefully the fact I'm used to business meetings and having to speak up and not, at the same time, cause chaos, will help. Hopefully