It’s not exactly the sentiment I have a problem with. There are definitely people who aren’t worth engaging with and there’s a time to walk away, as someone else in this thread pointed out they do. Responding in a kind of snarky, condescending tone rather than just walking away does not help you.

Think about an online thread where this happens: Someone is making an argument, and a troll appears. They engage for a bit, but realize they aren’t going to make any progress. Walking away let’s the thread die, and people who stumble upon it in the future will likely recognize the troll for what they are and consider the argument. Responding with condescension instead makes the person appear to only be arguing for self-aggrandizement rather than to actually help or improve anything, and it can poison the argument they made before. It plays right into the troll’s hands.