> they've been working that way for every other medium. Some movies are good, some are full of sex and gore. Parents have the responsibility to keep their kids from watching movies with content they don't want their kids to see.
Movie theaters and video rental places tend to refuse to serve minors for X or R material, and (if they look quite young) even PG-13 films. Stores may and often do refuse to sell R-rated films to minors. It may require active parental assistance for a minor to see those kinds of things (before the Internet, anyway—which is kinda the point of this whole discussion) and, even if enforcement is imperfect, surely serves to limit how much of that material even a very motivated kid can practically see (again, pre Internet, I mean). Also, kids have to get to those kinds of places, which can be pretty damn hard for them to do without a parent at least knowing they're out doing something, if not specifically what.
Broadcast TV stations risk FCC action if they show anything too outrageous when kids may be around, and have further restrictions even in night-time hours.
These behaviors are due to a combination of actual government regulation, and ongoing or historical credible threats of regulation if these industries didn't police themselves well-enough, which prompted the creation and enforcement of things like the MPAA's rating system (plus some now-defunct frameworks like the Comic Books Code or the Hays Code, both of which were much stricter than anything we'd likely accept these days—but for the "what's historically been within the Overton window of the freedom-loving United States?" perspective, those aren't that old and did co-exist with and apply to modern mass media, so still have some relevance).
The closest analog we have that I can think of is cable TV, since it's in the home and offers a whole lot of content, and even that tends to self-censor to a substantial degree and doesn't offer many of the worst things the Internet does at all—even on premium channels, which are another thing an adult has to actively work to bring into their house, totally separable from the rest of what cable offers.
Libraries are less-restricted and librarians seem to enjoy providing things a bit subversive (which is great) but I bet even lots of librarians would ask to talk to a parent before lending out certain books, let alone R-rated films, to young kids.
Support from outside entities—including, and largely, due to government action or threat of same—for parents to control what their kids see and hear is, as far as I can tell, the norm since fairly early in the days of modern mass media.
It's the Internet's model that's an aberration, requiring parents to take active steps to keep prevent kids from seeing hardcore porn or extreme violence or whatever on the same device they have to use to do homework, rather than having to take active steps to enable seeing those things, as they'd have to in most other contexts. Isn't it? Which doesn't necessarily mean these kinds of measures are a good idea, but I don't think "parents have always had to actively work to keep their kids from being exposed to awful stuff without substantial help from government and the private sector" really holds up, unless I'm missing something.
The Internet's unprecedented in its reach and being something that's basically required in a modern household, and required to allow kids some access to (again, it's not really optional for school anymore), but even other far less necessary media have had effective, if not perfectly iron-clad and universal, age restrictions imposed by businesses and the government. Right?