“A pipe gives a wise man time to think, and a fool something to stick in his mouth.”
Seems to fit here 
On the supply vs. demand side … I think of it as analogous to the mass shooters: it’s the person who pulls the trigger and the firearm that gave them so much incremental lethality.
Facebook, and the other dominant social media platforms, gave just about everybody on the planet nearly equal reach – an almost unlimited potential audience. This is a far cry from what survivalists used to do from the boonies with a mimeograph machine and a roll of 12c stamps.
The schizophrenic homeless guy standing on a corner with a sign and yelling with a hoarse voice has less reach than the huckster in a suit with his own cable televangelist channel on Sunday morning.
The unfettered free market, to me, has always been the equivalent of letting your children raise themselves. Maybe Zuck was greedy. Maybe he was naïve. Maybe a bit of both.