I once saw an official Facebook blog post about some change to the T&C, with 80,000+ comments on it, most of them one of those meaningless copy-pastes about how they don't consent to Facebook using their data. More comments were appearing every second.

Every 20th post or so, someone would be saying something like "Stop it you idiots, this stupid copy-paste doesn't do anything, you can't declare your rights like this." Then a bunch more copy-paste comments would appear before the next person telling the idiots to stop.

Would the segment of users who respond to content-free posts like these have much of a reaction to a comment saying that?

I don't mean that as a snarky dismissal, but a sincere question. I know that plenty of people, especially among digital-natives, have instant negative reactions to being reminded of data collection. But the type of user answering "what was your first car" or "what do you call your grandchildren" do not strike me as having much overlap with the groups that are cynical about social media platforms.

I don't really think it's a legitimate or scalable way to inform people. On a smaller scale it could help people in the local social network to be aware of what those posts are doing.

Another thing to do is to tell people "they're trying to use this information to get into your bank account". That will make them stop really fast. But as far as scalability goes, I don't think there's a way.