Not every parent knows how to enforce that kind of control, and no matter what you do, there will be loopholes.

Bajillion porn sites blocked? Oh look, he's now getting his porn off a Telegram or Discord channel! Blocked those, too? "Hey, school friend, can you email me some stuff? Yeah, my parents blocked nearly everything, only email opens"

As the other poster said, the only thing parents should not do is facilitate access, encourage or show porn to their kids, for obvious reasons. Ideally, parents should educate their kids, "Yeah, that stuff is for show, actual sex is very different. Work your cardio and don't skip leg day if you wanna impress your partner when you start having sex. Use a fucking condom, too."