It is rude, but it's necessary. Despite its pretensions of civility, Hacker News is not a truly civil place. It has it's fair share of trolls, cranks and sociopaths who will gladly spend hours stonewalling, derailing and sea-lioning you, just to piss you off, or score an endorphine hit from you. Many people aren't here to talk to you, so much as talk at you.
You have to learn when you're talking to one of the rare people who are interested in anyone but themselves or anything but their own point of view. As soon as you realize the other party is acting in bad faith, or you feel like there's little chance of further conversation not becoming hostile or just going in pointless circles, just leave.
That is the only way to stay sane here and avoid futile attempts at conversation degenerating into flamewars.