When people don't argue in good faith, I think it's more important to make sure others following along see so and aren't misled by FUD and ignorance. I value that over being sensitive to the person who is participating in bad faith, as this user is.

Being pleasant and gentle to everyone is not the most important part of discourse, not even on HN.

As to the accusation of ad hominem: every single point I made was directed at - and based solely on - the arguments made by the other user. Once these arguments were ultimately found to be made in bad faith, I ended the discussion. That's not an ad hominem argument, that's ending an argument because of a negative evaluation of the other person's state of mind. Two very different things - almost unrelated, honestly.