I would say that up to the point when they started for forcefully manipulating their content for direct payments or indirect "retention", yes, the benefit outweighed the costs.
By 2015 they were almost all incredibly harmful and mostly valueless.
As a Black person in America, I'm not in the slightest. Documented and spread proof that "we're not crazy, look at this stuff that actually does happen."
And a LOT of bad.
Overall, do the costs of global social networks outweigh the benefits? I'm skeptical.