- Avatars. A consistent, recognizable image can go a long way from transforming a faceless internet post into something closer to a person you recognize and would hesitate to harm. With enough time and exposure, usernames can work for this (everyone recognizes when tptacek, or moxie, or you post), but avatars supercharge it. People hate changes to the site UX, so maybe put it behind a profile option that's defaulted to 'off' - then, only people who care about seeing them do. Of course, this would increase the moderation burden - people using offensive avatars, etc, but I think it could help.
- Heads on pikes. A weekly/monthly/ongoing/whatever roundup of notable bad actions which people have been moderated for. This should be limited to interesting and informative cases - not spam, piracy, CSAM, etc, but legitimate humans engaging in bad-faith actions, flame wars, etc. Having negative examples to avoid can help a community understand what is and isn't appropriate in a more concrete way than a dry set of rules. And seeing people be punished for violating those rules in a public way can have a deterrent effect. Making these public works better than just downvotes, because downvotes ultimately end up hiding content.
- Exemplars on pedestals. The obvious counterpart to negative examples is positive examples. In a way, the upvote system already does something like this, but it's not the same as officially-sanctioned recognition from the staff. A very simple approach might be to give you / other staff members (maybe even high karma users/yc founders) a button on each comment that highlights it as a positive example worth emulating - maybe changing the text color in css of the username/time stamp to show that it's been recognized.
#3 I think is a good suggestion though. We should have some means whereby users can exalt something good, not just flag something bad. The challenge is to make it different enough from the upvoting system so it didn't just turn into a variation of the same mechanism.
The UX for paginated threads is awful. I know you want to get rid of it, but I really hope you don't, because reading through something like the 4000 comment Biden thread as a single page would be incredibly taxing, and having to go through 'more' links to get to recent content is annoying.
Long threads do need to be paginated, but I think you should consider what other forums do and add a set of page links at the top and bottom of each page. It would be slightly more clutter but you wouldn't have to remind people that paginated threads are a thing every time it happens.
Better links for navigating around large threads is on the todo list too...
Threads aren't linear - people don't read them from top to bottom like documents. Every subthread is a separate conversation which the reader may or may not be interested in, and having distinct pages makes discovery easier. Ask yourself why every other list page on the site is paginated? Why have only thirty stories listed on the front page? Why not just list every story ever posted, or every story this year, or the first thousand or hundred at a time?
And as far as "one can simply stop reading," ... yes... but this is a forum. It's primary purpose is to be read, not to demonstrate how quickly Arc can render HTML and send it up the pipe. That isn't even impressive. What is the value added by rendering a thread in a single page? How does that make the site better than pagination? What is the user getting in return for the loss in readability?