Speaking as someone who deleted his Facebook account years ago, a positive that FB brings to the world is ubiquitous and easy sharing of personal information with the public. With an FB account, you can keep in touch with even casual acquaintances, perhaps forming a connection. That's pretty deep, and a net positive for humanity, and fulfills the promise of the internet.

I predict that what we call "social media" today - this specific aspect of ubiquitous human connection - will continue long after FB is gone and forgotten. I foresee that the ultimate successor will likely be more of a protocol like RSS or FOAF that various platforms can plug into, rather than another web app you log into, owned by yet another monetizing corporation.