> content that makes us angry, anxious or jealous is a much better driver of clicks than content that makes us happy

This might be true. Or it might be a belief we formed to explain Facebook's behaviour, and we now need to start updating our beliefs.

Anyway, assuming it is true, Facebook still must balance two things: (a) get clicks from your existing users (b) get and retain users. In their halcyon days they could take (b) for granted. Perhaps now the market demands some humility from them?