And we can even go further back; have people checked, old black & white cartoon? Some of them are so blatantly propaganda/politica/visual horrific that they wouldn't even be aired for 15 y.o today. If you take a closer look, even Tom & Jerry is quite violent, and most Japanese animation that air on kids TV-channel back then also, very sexual.
And these things were airing on TV, broadcasting at a specific time and all you had to do as a kid was to push a couple of buttons to access it.
You couldn't see the surveillance footage a guy being dismembered by a lathe or weird Japanese rape porn in 1080p by "pushing a couple of buttons" before the internet. Well, at least not where I grew up...
Aside from the psychological differences with teens, we also have to consider that they aren't being exposed to this environment "in moderation". They don't really have the opportunity to think about their responses to it.
That, and the pervasiveness of social media. Myspace, for example, was huge. But unlike today’s social media, maybe 25% of your AFK circles would hang out there, not 95% like today.
During the early years of the German equivalent of high school, most of my classmates would spend days without being online once.
Ouch. Right in the nostalgia :)
I'm pretty convinced that just a "dumb" web 1.0 site of shocking content is way better for your mental health than a handful of giant corporations honing in on your psyche and exploiting the weaknesses of the human mind.
So while I very well remember goatse, tubgirl and rotten.com, I only discovered those as an adult.
Also note that I wasn't singling out social media here. It's the web as a whole that seems very unsuited for a teenager without supervision, IMO.
I'm 30, so myspace and Facebook showed up only once I was in high school, but everything you describe was still available on the web before social media. Shock sites were huge (goatse, tubgirl, etc), and I remember watching a beheading with a chainsaw by a Mexican cartel. And of course porn was around too.
The difference with social media is the "keeping up with the Joneses" except now it's your entire life, not just your literal neighbor. Way more damaging long term, since you actually know these people and can relate to them. Yeah the beheading was shocking, but I'm not hanging out with cartels regularly. Just a completely different thing.