I tried this trick once, but I failed because I was in Australia.

There’s always a reason, but it doesn’t need to be entirely rational. Kellogg was a nut, but that’s a different topic, no?

Thanks for citing this, but it still doesn’t explain why this custom has developed.

The only system I’ll accept. Not necessarily for pornography and a lot of “save the children” claims are just pretext for privacy violations, but there are services that legitimately need to check some info and a zero knowledge approach is the most privacy preserving way to do that.