There's no real limit to what bad-faith actors will use to appear legitimate. They'll use philosophy, science, religion, etiquette, etc - in constrained, self-serving ways, of course. We can't just assume anyone doing those things is evil and acting in bad faith - otherwise we're just elevating the ad hominem as our supreme, central dogma.

That seems to imply an assumption of lack of good faith, unless I’m misinterpreting what you’re saying.

While there’s no doubt that one can find cases to which this applies, I’d think that applying that broadly to the vast majority of people who are arguing in good faith would stifle debate.

I have no objection to ignoring etiquette in general. The point I was trying to make is that treating etiquette as ethics is how people justify shutting down debate on controversial topics. They also use it to dehumanize their opponents on an issue, and that is unethical.