> why does it matter what Mosseri thinks? It doesn’t surprise me at all that [tobacco executive/drug dealer/social media executive] is downplaying their negative effects on society

It might not surprise me. But if Philip Morris started arguing nicotine isn't addictive, I'd assume they're no longer able to run their organisation without increased public oversight.

> Isn’t it up to the parents to limit social media use?

Sure. One way parents can do that is by encouraging their represenatatives to pass laws to protect their children.