Oh, the communities I'm a moderator of (all webcomics related :)) have so far not had any conversations of this type at all, and are incredibly low maintenance, so it's a hypothetical worry.

If that's not your community, then maybe the solution is to post only when you have a few extra spoons, just in case, and when you see something problematic, state why it is at the same time you say it is, and only do so when you have enough spoons.

That's what I try and do, but sometimes it turns out that I either misjudged my spoons, or the situation spirals into a spoon swallowing mess :( I think I'm just not going to post to places I can't control so much, it's all too fraught.