I think one of the things that makes HN and Reddit very different, is that the content is not personalized and tailored to maximize user engagement. Facebook seems to constantly show me things that make me more upset or concerned or outraged about something. I remember reading articles documenting this effect, but I can't seem to find them now.
The other type of posts I tend to see are about friends bragging about how many km they ran today or how great their vacation was. Not that it's that bad to post these things, but I wouldn't be surprised if exposing yourself to them constantly increased feelings of jealous and reinforce one's need to compare oneself to others.
On the other hand, I've discovered a lot of interesting books and projects through HN and learned about different topics, since there seem to be a lot of knowledgeable people here that comment on topics I know nothing about. The only type of posts that may be prone to making others feel worse are the ones about salaries / financial issues, but they are not that common.