I agree some of them are obvious trolls, but being respectful isn’t only or even necessarily to benefit the two parties, but also everyone else who is watching the interaction.

It’s never just one interaction though. There’s others in the thread whenever this happens, and those others typically have good faith people in them. Those sections of the thread produce something completely different.

I’m not going to be respectful to people engaging in unproductive and bad faith ways. They are not being respectful, that deserves calling out and dismantling. Standing around and respectfully allowing someone to run their bullshit all over you results in giving the impression to third parties that the things they say are deserving of respect. And given that most of the time this is gish gallop lists of communist crimes and supposed genocides giving people the impression they deserve respect is a poor move with an observing audience. You just resign yourself to a situation in which you’re individually examining one massacre after another explaining why it is or is not bad and get caught up in time wasting bullshit instead of doing anything productive.