Not to be to overly reductive, but you could use the same argument for drugs and weapons.
It's just selfishness. "I want some privacy utopia on the internet (which can no longer exist, the internet isn't the place of the 90s and early 00s), so your kids can be exploited by social media and porn".
I know several parents that limit screen time, require screen usage be restricted to public areas of the home, have parental controls and filtering operating etc.. some of the parents I know won’t even let their kids watch a movie unless they screen it first.
Actually not, since I use Linux, but most people's do. It's much worse on my phone.
The internet can also contain potentially very bad decisions.
I don't want to argue to block the internet, but it is just not black and white.