I think that's a subjective line. It's easy enough to get in a mindset that anyone that you disagree with to an extreme degree is just trolling, but I think we're all better off not assuming that too early. I was attempting to redirect the discussion in a productive direction, and did stop after it became abundantly clear that wasn't going to happen, but I'll readily admit in hindsight it probably went a comment or two farther than it needed.
I can't reply it won't happen again (I'm an optimist at heart, which is part of the problem in this case), but I can say I do try hard and I think mostly succeed in reigning those impulses in, and I like to think it's somewhat rare (at least to this degree).
"Don't feed egregious comments by replying; flag them instead." (a.k.a. please don't feed the trolls).
https://news.ycombinator.com/newsguidelines.html