I think it's the standard social media stuff - pseudo anonymity, lack of nuance or easy clarification, lack of private conversations meaning everything is exposed to the lowest common denominator.
Not saying HN is particularly bad as social media goes, but there is a big difference between having a chat at a bar where you adapt to your conversation partners and have a mutually interesting discussion while being mostly diplomatic, vs posting something for posterity where everyone that passes by can give a hot take or "what about", "source please", "explain what you mean by"...
Your comment is actually a (very benign) example - I don't mean offence, just saying that the gp put a comment out there and now it's available for anyone to come by and jump on, where the dynamic would be different in a pub convo
Physical locations also tend to force me to engage back- if you say something I disagree with, I may not speak up, but my reaction (or lack of reaction) communicates to some extent what I think. Online, I could be annoyed by you, or happy that you think like me, or seething mad, and no-one may ever know if I choose not to.
I don't think HN is generally worse than physical interaction, but it has the potential to be. Social environments often have some moderating influence on participants, through social customs, lack of anonymity, and better communication through body language, tone of voice, etc.
Overtime, making in person, physical connections with people can be crucial to your long term well being.
This community wouldn’t fill any gap related to human suffering that real humans do.
According to Oldenburg's criteria HN doesn't really fit.