That and there isn't really a universal adblocker for mobile yet, so there is no way to get around them shoving poorly targeted ads in your face relentlessly.
That can't be good for the mental health of younger people in general. Idols are easy to fanaticize over; not just for teens, but for adults too. HN is a testament to that. But then again HN is a testament to a broad set of fucked up things in general.
I can see how the sniping from random strangers on a near constant basis would cause issues, because there are less and less actual "communities" (ala IRC channels, forums, etc) being formed, it's more of a anyone-can-drop-in-post-and-leave situation because, well, that's the nature of these platforms nowadays. There is no encouragement to build some kind of a conversation with any particular individual beyond the current post/thread/whatever.