TBH I think this is all either fundamentally flawed or incredibly weak except for your final paragraph. That one actually poses a somewhat interesting question - why the seeming disparity between online and offline porn regulations in the US? Still, it fails to address (or even acknowledge) the differences in the impact of requiring ID between those scenarios.

Also I think you have this entire thing exactly backwards. It's not on the rest of us to convince the other camp that ID shouldn't be required. Rather it's on the other camp to put forward a convincing case that ID should be required - that there is no realistic alternative and that the tradeoffs are worth the cost. Otherwise the current status quo wins out.

> Self categorization has been the status quo since the 90s and has been proven to be insufficient.

What are you on about? Legally mandated self categorization has never been tried and would presumably work if there were penalties for violations. You don't even need 100% compliance, you just need high enough compliance that the default becomes to filter out any site that fails to do so.

Voluntary self categorization isn't particularly useful because almost no operators bother to do it. So you're left with no (workable) option other than whitelist filtering.

> have a third party come up with a solution that people can buy to filter us

I never suggested anything of the sort.

> The liability belongs on the people dealing in the restricted item.

The items are not currently restricted and I don't agree with you that they should be. However I would agree to changing things to make all providers liable for accurately self categorizing the content they serve up by means of a standardized header format or some other protocol.

> Why is online ID verification a problem for e.g. porn and gambling but it's fine for alcohol?

Presumably because you have to take receipt of the shipment so the vendor is already going to collect your PII.

Why is legally requiring that a gambling website send a header categorizing itself as such unworkable yet somehow it's all going to work out just fine if we require them to do the much more complicated thing of securely handling and accurately verifying identification documents? That seems like an obvious contradiction to me.

> Why should it be fully anonymous? Should we also allow anonymous porn and cigarette vending machines in person?

Don't we effectively do exactly that? There's no requirement for ID retention on sale of alcohol or cigarettes and until recently the norm was for the clerk to briefly eyeball your license. They also didn't used to bother checking ID if you looked old enough. (That's changed at the major retailers around here lately but that's a different matter.)

Anyway I never claimed the brick and mortar way of doing things was ideal so arguing as though I've agreed to that seems rather disingenuous.

> If you're an adult and spending money online, you already told them who you are

But I did not give them a copy of my ID or any otherwise unnecessary PII and do not want to be required to do so. Also there are plenty of ways to pay for things online without readily revealing your identity to the couterparty. I expect you are well aware of that fact.

> Why is an unrestricted public website different?

For practical reasons I'd imagine. Analogies are great and all but at the end of the day a global electronic communication network has rather different properties than a physical brick and mortar location that you walk into.

Regardless, the reputable services all seem to agree with you (as do I) and thus go out of their way to send headers marking them as adult only. It's roughly equivalent to a shop hanging a "no under 18 allowed" on the door but then not bothering to ID anyone. If parents can't be bothered to configure even the most basic of controls on their children's devices why should the rest of society be made to suffer for that?