There’s a basic expectation, when you make an argument on a public forum, that it’ll be judged on the content of the argument, not on who posted it. If you want to look through their history to see if they’re a troll, and then just ignore them if they are, there’s nothing wrong with that.
What you did was say “you’re stupid and lazy,” but for no good reason, you used that guy’s own words to say it. That was entirely unnecessary. It didn’t prove any inconsistency, it just proved that, like many people on Lemmy, the guy thinks a lot of people are dumb.
What is non-toxic about using someone’s own words from past threads to insult them when you already have enough of a text wall to make your point?