The point is that it is unrealistic to expect millions of people to mark the content. Also, the header is better than the metatag because it can be added to images, videos and other non-HTML content as well.

I tend to agree - making folks intending to interact with minors comply makes more sense.

That said, outside of the merits of this approach, I am dubious of any actual implementation given 2 points.

1) Protecting the youths will always be a leaky bucket. With disadvantaged youths possibly more at risk. Those exposed to non-compliant parents ("cool" parents who are ok with sharing unsuitable content) or lacking strong parental involvement, likely won't benefit a great deal from any implementation.

2) Anti privacy social networks stand to gain the most from targeting ads utilizing signals from most child safety acts. They also might be able to reduce some costs from moderation if they can make it someone else's problem. I'd argue the net social impact from these social networks is likely both more normalized and strongly negative for our youths than any smut.

On the balance I'd say we are better off investing our energy in other places.

The header (for videos and other) was mentioned in [1]. I agree that is the way to go.

Adding a header to a web server or load balancer or app server if done globally can be done in a minute or two. Maybe 5 minutes for the intern not counting QA testing.

But you are right, the inverse is easier. I like that too. That was debated in the other recent thread.

[1] - https://news.ycombinator.com/item?id=47950091