Pornhub has to save itself from government regulation that has been on a mission for a decade. They did it to appease the politicians. I think at 18, you should be able to drink and smoke if you want. The nanny state has become very prevalent in America. Weirdly the conservatives are pretty cool with it.
I think in every state people can smoke at 18.
Porn addiction, like any other addiction, produces tolerance with repeated occurrence.
The brain becomes trapped in a futile and often endless pursuit of reward.
It leads to successive decline into deviance, eventually child porn.
This is one of the best, though not the only reasons to outlaw porn.