Earlier quoted context omitted.
"How long and often" people engage with content is a perfectly reasonable metric to optimize and a very close correlate of interest. There are, in fact, plenty of things going on in the world people should get mad about, or that they should worry about. Some people think that's climate change, some people think that's migration, some people think that's rising fascism, some people think that's Mamdami opening grocery…
None of that addresses whether Facebook is intentionally trying to sow discord and make people depressed and anxious for profit.
For example, are you suggesting that Facebook begin censoring information about the climate emergency because it makes people depressed and anxious? Should Facebook make sure that people don't see content they disagree with, because that promotes discord? Or is it the other way around - they shouldn't see content they agree with, because that creates an echo chamber which increases discord when they do encounter other views?