The only hard part for the web is that a site could lie since there is no gatekeeper, but some black lists can help with bad actors.
Websites by default are ‘true’ for every category, unless they specify.
Categories are, for example of some: nudity, sexual, violence, etc.
It doesn’t have to be perfect but sites will have to err on the side of caution.
We could even create an html tag <restricted type=violence> for example, and the browser can simply not render that portion of the page of the user has that type disabled.
And we could give companies a pass for best-effort categorization using tech to assess user-generated content, along with allowing users to flag their own content as “safe”
The goal should be to satisfy most reasonable governments. A neutral technical standard and an international organization to maintain the the ontology for content descriptors
There's no reason a simple, standardized header can't be used to communicate any number of classifications simultaneously.
Edit: It occurs to me that if you oppose all age related measures then my above response isn't entirely fair to you. I still think it's an absurd objection but the comparison I made no longer applies.
What we need regulation to provide (IMO) is a reliable way of doing that.
Sites can choose to have unrated content (adult movies) and those are only available on devices without an enabled parental control option (adult-only theaters).
A solution would be browsers refusing to load any site that didn't provide such metadata, not just in child mode but in any mode. I suppose either Apple or Google would likely be capable of unilaterally imposing such a requirement as things currently stand. However I also think that's unlikely to happen on its own for various reasons. Thus legally mandating certain basic content classification categories in addition to an extensible standard protocol for communicating such metadata would (I expect) end the cycle. And rather than the government going after individuals the legislation could be structured to place the onus on mainstream browsers, OSes, and other client software to enforce compliance on their behalf.
Fine. It probably should be, if sites don't want to bother cooperating.
With a universal labeling standard the UX would be much better, and there'd be a much greater incentive for website owners to participate (they'd be implementing a universal standard, not adding support for one particular parental control tool).
For example, it would be insane if every website and blog in the world to had to run logic to detect and prevent Elbonian males under 16 lunar years from seeing ankles except on Thursdays.