If you want to say something, say it. Don't say the opposite in a sarcastic tone.
Edit: ok, evidently jokes aren't a popular mode of speech either.
Of course you can easily overdo it but I think banning sarcasm has a significant downside and we should rather teach people to use it correctly.
What the commenter was doing was insinuating a conclusion based upon a straw man, so as not to be scrutinised for the underlying conclusion.