I don’t know if this is the case for other people, but I have to be careful about using slurs in any context because the more I see or use a word the more likely it is to slip out in other situations. I’d never purposefully use a slur on somebody, but my word-choices are largely running on automatic when I’m angry. I just push intent at my mouth and then my subconscious picks out words matching that intent and feeds them into my tongue. If I push the intent “strong targeted insult” into that system, a slur could match those parameters and make it out my mouth before my conscious mind can catch and filter it. Entirely avoiding using slurs, and ideally avoiding even thinking slurs helps to avoid this happening (both by avoiding them entering my vocabulary-supply in the first place, and by building the mental reflex to immediately drop them like they’re hot if they do pop into my brain).

A more society-level reason to discourage people from publicly using slurs even in discussions about them is to make it harder for bigots to stage “discussions” as excuses to loudly use slurs while in earshot of the people they’d like to use those slurs at.

People also get paranoid about automated (or braindead) moderation, or trolls who shame people based purely on the fact that a quick and context-free search of their post history turns up N uses of a slur. It’s often easier to just dodge these kinds of problems than to fight them.