That was our struggle with implementing "blocking" tech at a school I worked at. Is a kid looking up how to do a breast self exam porn? What about a self testicular exam.. What about actual Sex Ed kinds of sites?

That's between parents and their local governments. Yes when I was a kid my mom let me watch whatever and go wherever. The parent in my example ultimately decides what a kid may or may not do which is in alignment with existing laws. If the parent is endangering their kid that is up to them and their government to sort out.

Point being, put the controls entirely into the hands of the device owner. Options can be to default to:

- Block everything by default unless header states otherwise.

- Block only sites that state they are adult.

- Do nothing. Obey the operator. (Controls disabled on child accounts or make them an adult or otherwise unrestricted account on the device).

I think the options are just limited to our imagination.

> I know parents who have no problem with their kids seeing porn.

Surely you mean at least teenagers, and not literally children, right? Consider the prevalence of violence, racial stereotyping, and escalation of fetishism into degeneracy that clearly exists within this medium; what's the line that these parents draw? Are they making sure it's only something vanilla? Or is there no line whatsoever?

Then those parents can turn off their browser/client’s age protections. I think that’s actually a decent argument for the solution posed by this thread.

There are already laws defining this. Had to draw the line somewhere, and they did.

> I know parents who have no problem with their kids seeing porn.

I don't agree with showing actual children porn, but I also totally expect teenagers to find some way to get access to it in the age of the Internet.

Part of the challenge with this is cultural. Different places in the world think about sex, sexuality, and even the concept of what is a child differently. In the US, showing a woman's bare breasts to a person under 18 is generally considered wrong, and in many cases is illegal. In most of Europe it wouldn't even raise an eyebrow, because bare breasts are on television, sometimes in commercials even.

Set aside for a moment the question of age verification and age limits, we cannot even agree in any sort of universal sense what even qualifies as porn or adult content, and at what age someone should be able to see it. There's a difference between a 7 year old and a 17 year old seeing the same type of content, and there's also a difference between a photographic nude and a video of people engaged in coitus.

The story is basically the same for everything else you listed.

These age verification laws in many ways are trying to use the most heavy-handed mechanism possible to enforce American cultural norms on the entire planet. That's clearly wrong to do. What the GP suggested using RTA headers though puts the control into the parent's hands, which is as it should be.