Absolutely, the idea that a naked human body is inherently obscene, and that we need to protect people from viewing it, is ridiculous. It's the sign of an immature society whose practices are still based upon ancient superstitions.
Fucking (typically) happens in the context of nudity, but there are many other reasons for nudity, and its association with and only with fucking in American society has led to some...unfortunate side effects.
It's interesting that you're using active language ("pushed on") for kids browsing and seeing something. It's possible (likely, even) that "Artistic nudes" should have an 18+ tag on them that 1. Prevents an under 18 user from seeing them and 2. Is easily filtered out.
I'm kind of astonished that isn't already the case.
But I also think one thing that's happening is a bunch of people are taking the opportunity of Twitch expanding what's allowed to flagrantly break the expanded rules. And it's always a little funny to me when people say "People are flagrantly breaking the rules! We need tighter rules!"
But 1 and 2 are not implemented. That’s the tablestakes.
It’s not ironic to suggest that this particular rule is prone to abuse and that changing it would change user behavior.