It's different. You show an ID card to a human if you don't look old enough. They look at it and return it. The ID card doesn't get scanned or tied to all your future recreational drug purchases - you don't have an account or a trail that identifies you.

When uploading ID documents, your account gets tied to your real world identity. That's not a precedent the government should be setting, because private entities having an excuse (the law) to require identification erodes privacy, and because in the future other services could be required to ask for an identification, too. Yes, it's the slippery slope (aka "boiling the frog") argument, but that's how laws that erode privacy evolve - step by step.

Now it's account for social media, then it's porn sites, then it's forums where you might see porn or discussions on suicide, drugs or anything deemed morally hazardous. They might require an ID just to view the site or require the site to not make it public. If (or "when", if we don't oppose such laws) enough countries mandate something like this, most sites will likely require an account for all content, regardless of where the person is located, as otherwise they'll likely have to prove that they've not only geolocated the IP of the visitor, but checked that they weren't using VPNs, Tor or similar services.

As for using zero-knowledge proofs and similar technology to make it less infringing on privacy - I very much doubt the government (any government) to implement this with 100% privacy and security.

Yes, but those are in the physical world. [1] In digital realm, having to verify your ID has way more consequences. My passport has been leaked and I have a “quick cash loan” in my name as a result of that.

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[1]: Tangentially, those are trivially circumvented in many countries. When I was a teenager in St. Petersburg, we’ve used a “duty free delivery service”, which (I suppose) just stocked liquor at the duty free shop on the border with Finland, and then sold it. Not sure how legal was the core premise (probably not), but we used it because their couriers didn’t even pretend they need to check our passports (definitely illegal).

In many countries, alcohol is available in grocery delivery services. Couriers happily leave your order at the doorstep even though they are supposed to check your ID. In many other countries, even buying in-store is possible (e.g. Japan, where in any konbini you can just press a button on screen saying “yes, I’m 21”).