Lots of good points here. I particularly like the "dark triad" bit, though I think a lot of nuance around different types of likes/upvotes/whatever is missing. It makes a difference whether those are shown to others and/or used to sort others' feeds. That last point is very close to montenegrohugo's about algorithmic feeds, with which I completely agree. Algorithmic feeds, especially those which show content from people/groups I don't even follow, definitely deserve a place in the Dark Tetrad.

To illustrate these points, consider HN itself. Yes, HN uses an algorithm to determine story prominence. Yes, it has upvotes. Yes, it uses relative timestamps. OTOH, the upvotes are not shown to others and it doesn't have infinite scroll. I also wouldn't consider it a "feed" like Twitter or Facebook. On the third hand, even the features HN does have arguably contribute to echo chambers and audience pandering. I think this well illustrates that it's not easy to determine good vs. bad social media, and it would be hard to argue here that all social media are bad. ;)