You don’t do that for the poster. You do that for other readers.

When someone makes a completely stupid comment, like “Drink bleach to kill viruses,” I won’t go and reply “no you wrong!” I’ll reply “For anyone reading, that’s a dangerous advice and here’s why [citations].” I don’t care if the poster then replies with “nuh uh, fake nooz.”

(I didn’t downvote you, by the way.)