There's a difference between 200 people in a square watching and filming you, and between an organization doing the same thing and then making it available to all of mankind for the rest of time.
As I said, I doubt it will happen, that doesn't mean it shouldn't happen.
If I ever have kids, I'll make a concerted effort with other parents to prevent them from joining any social media before they turn 16.
Honestly that seems unlikely. If all their friends are on some platform they will find a way to be on it also. Best you can do is really try to educate them on how badly things can boomerang and that the internet never forgets. But even at 16, most kids don't have the life experience and perspective to really understand this.
I'm afraid it really isn't the same at all. Even when I was 25 I did stupid things. I would get drunk in a night club, like everyone else in my age, and on our way home we might have a piss in the middle of a big public square at 4am because we were drunk and stupid. Does that mean I would also get my bits out in the middle of a public square when there are 200 people staring at me? No.
Doing or saying things in a public place != Publicly saying or doing things
You can do private things in a public place, and that's how many people with a very small following feel on social media.
Did we all do stupid stuff when we were younger: absolutely. Would I want the entire world to see what I did as a teenager and judge me for it? Absolutely not.
Which is EXACTLY why I personally think society should just not allow people under about the age of 25 to even be on social media in the first place. I know, I know, that will never happen because insert reason - but if we don't want everyone's actions to be recorded in perpetuity we should probably stop allowing them to post those actions in a forum that's open to the entire world and easily recorded. You can make laws until you're blue in the face, it's not going to stop an individual from saving whatever stupid thing you said or did and leaking it anonymously should the moment present itself.