An important piece is people using those types of tools to make an active and informed decision.
There doesn't need to be a hard and fast rule about kids not seeing R rated movies. A movie can get an R rating for merely having a few curse words, which is different than a movie with extreme sex or violence. I would hope that parents play an active role when it comes to what their kids watch.
A friend who is a teacher had to talk to his grade 3 class because they were playing games and pretending to shoot each other as an imitation of the Squid Game TV series. Elementary school kids do not need to be watching one of the most violent TV shows in existence.
Yeah, let parents decide for the most part by all means, but it should be acknowledged that many aren't paying attention and there is a line where I have no problem saying that yes, letting your kid watch this particular show at their age is bad parenting.