>Contrast that to Facebook or Twitter, where only positive signals exist, and the entire system is designed to surface "edgy" content as much as possible (because it gets the most engagement!)
But that's the same system used for link submissions? you can upvote them but not downvote them.
You can flag submissions, which works sort of (but not quite) like a downvote. Plus, there are some mechanisms limiting "edgy content", e.g. if the comments/upvotes ratio starts screaming "flamewar!", the submission will drop off the front page like a brick.
You're assuming what you see (eg lack of capcha) is all the protection that exists, and that there's no other protection. It's kind of like Disneyland - a lot of work goes into making the site what it is, and you don't see even a tenth of the work that goes on into making it look so good.
True but links are sorted in competition with other links with a zero baseline. Comments piggyback on the link popularity will always show up on the page. Exception of course the massive 100+ comment hot topics.
Thus links resting state is a quick falloff and death. In contrast comments tend to hang around, even bad comments if they are part of an interesting conversation.
But that's the same system used for link submissions? you can upvote them but not downvote them.