Alcohol is bad health wise but probably is used to reduce the harm of social imposed stress between people.

So, If I think about it "like alcohol", it would mean "what is the root cause of not being able to keep contact with people". It might be that common social mixing places are probably much fewer than hundred of years ago - be it the local bar, gathering after a day of work in the field, public bathhouse, etc. Many of activities in the modern world seem very individual - maybe that is the problem, and people being social try to replace it and get tricked into worse things.

The difference is the "algorithmic" timeline (meaning ads) you get with Facebook, Insta, and co compared to the strictly chronological timeline you get on the Fediverse equivalents (Mastodon, Pixelfed). That it's less addictive, or at least not in the doom scrolling type of way, is more a consequence. Aka the enshitification argument.

Masto specifically is also a Twitter not Facebook replacement, with everyone soliloquizing past each other rather than holding a genuine conversation.

For the actual "good" Facebook use cases such as keeping in contact with school/uni veterans or other closed group, there's friendica, but it's nowhere near Fb in terms of volume.