I would guess that any community becomes an audience at a certain point. It's like having a wedding. You (probably should) love and admire everyone there, but if it's large enough, it's really hard to offer up much of your attention to everyone in gratitude for sharing the moment with you.
Either way, these algorithms definitely put their crosshairs on anger. Happy people aren't very motivated to action.
Yes, but the community still gathers to share a positive experience together, even if just for a short period of time. There should be more shared positive experiences, but online, I think it is the reverse. Anger is more actionable than happiness it seems.