I also see and give a lot of academic presentations, and I'm not aware of any venue that encourages someone from the audience to commandeer a talk. "Let's take

I also see and give a lot of academic presentations, and I'm not aware of any venue that encourages someone from the audience to commandeer a talk. "Let's take this offline" is so common as to be a cliche, and if the speaker got flustered enough to get caught up in it, a decent moderator steps and makes that call. There are many reasons for this. One is that it's simply the polite thing to do. Another is that the audience may want to hear the talk rather than whatever particular point you're hung up on being the only topic of conversation. Yet another is that it's very unlikely that the speaker has absolutely nothing of value to contribute, so it's in everyone's best interest that emotions have a chance to cool down a bit rather than the speaker deciding he's never going to talk to that asshole from the crowd again. We weren't at this meetup of course, but it very much sounds like that's what should have happened here and didn't. I'd also point out to anyone thinking that being right is an excuse for this sort of behavior that people will remember you being an ass long after they've forgotten you being right.