Metaphor time:
Consider a liquor store in a physical space, and a porn site on the internet.
The liquor store requires ID at point of sale because it has limited entry and exit into the building. It has physical restrictions making it harder for minors to enter, and harder to exploit their way into accessing age-restricted items. This is because the physical world is always shared by default, and we must make rules securing adults-only spaces in a world that’s intrinsically shared with children.
A digital porn site exists on a realm solely built by adults, that requires adults to access in the first place. A child cannot sign up for an ISP, a child cannot buy their own cellular phone[1], and a child cannot decide to share their coffee shop or library WiFi for free to everyone within range. At some point, a child requires the assistance of adults to enter the internet. That makes the internet a de facto space for adults first, not children, and that is why I vehemently disagree with vilifying the majority of users (adults) just to “protect” kids who will bypass those age checks like they’ve successfully done for decades.
There will always be youth finding a way to procure pornography, drugs, or alcohol underage. The difference with the internet is that it’s by adults, for adults, and that children are guests who should be supervised by adults in their circles - not by policing all the adults online through intrusive surveillance measures.
[1] Children can, of course, use cash or cards to buy prepaid phones and airtime in many countries. I do not think this should be allowed and would be a better venue to restrict access than a surveillance state.