I can't say whether banning kids from social media *is* actually good, or bad. It's a nuanced thing, and I'm not even close to having all the thoughts marshalled on the topic.
But I can speak on one facet.
My school used to block various sites, hold down the network, all that kind of (smart, reasonable) stuff.
What this did, was make me (and a handful of my friends) pretty good at evading network security. Not 1337 hax0r type stuff, but... good enough.