That's the point. From a moderation perspective, comments are at least partly responsible for the subthreads they spawn: https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor...
The GP was well-intentioned but unfortunately that's only a precondition for not starting a flamewar. It isn't sufficient: https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so...
Btw, I don't think it's quite true to say that the touchy subject was part of the article. Even if it were, though, the burden is on commenters not to take an HN thread further into flamewar. This is in the site guidelines:
"Comments should get more thoughtful and substantive, not less, as a topic gets more divisive."
"Eschew flamebait. Don't introduce flamewar topics unless you have something genuinely new to say. Avoid unrelated controversies and generic tangents."