In the absence of social media, do people simply replace their wasted time there with leisure like video games, television, texting, and the like? If yes, the net impact of Facebook is small.
Or, have the addictivity wizards actually managed to increase the amount of time spent in leisure, taking away from familial connection and deep friendships?
With Facebook in particular, there's a generated sense of belonging that comes along with the quantified social proof which makes the hits of dopamine much more personal and meaningful. I see this as trading off against getting that sense of connection in reality.
But much of the other 'damage' from Facebook is fungible, and people would turn to other sources of leisure and addiction soon after losing it. Perhaps one day these addictive engines will be powerful enough to make this untrue, but we're not there quite yet.