This is exactly what I meant by my above comment: It’s like the pro-ID check commenters have become completely disconnected from how young people work.
Someone’s 18 year old sibling isn’t going to be stopped by “should know better”. They probably disagree with the law on principal and think it’s dumb, so they’re just helping out.
But imagine if a locked device was treated like alcohol. Most kids get access to alcohol at some point despite it being illegal, often from older siblings, and rarely with legal consequences for the adult. But it's much less of an issue, because most kids don't get it consistently. Furthermore, "good" kids understand that it's bad, and even some "bad" kids understand that they must limit themselves.
Is it though? When older sibling helps younger sibling with "accessing Steam", or something reasonable like that, even the most sensible and thoughtful older sibling won't be interested in "culture shifts" that block gaming fun.
The alcohol and seatbelt analogies try to elevate equivalence, but miss the mark by a lot. Even one drop of alcohol is obviously not suitable for underage. No seatbelt increases risk no matter your age. "Social media" exposure for the young person is often completely fine and full of "young person" content and activity.