I'd tentatively say, casually available heroin, morphine and laudanum/opium.
It obviously caused problems and pushed the market underground but it seems to have worked out.
I'm not aware of any studies in to this though, so it's only conjecture/guesswork.
I'll also clearly state I'm not putting them on the same level as this current dystopian bullshittery.
Fair enough, came in a bit hot there, my bad.
I'd argue that it not being a legal threat doesn't matter too much in this case because they aren't looking for legal control, so much as "effective" control.
If they can stop you without needing for it to be signed in to law, then they'll take that, if they can get a law as well, then I'm sure they'll take that too.
Censorship isn't a binary, but we can agree to disagree on that one i suppose.
To this part though
Not really, there are numerous titles available exclusively on itch.io and steam, those are effectively censored by your rationale as you can no longer purchase them at all.
Honestly steam gift cards don't work at all here because it's not a ban on buying the games using a card, it's a ban on steam listing the titles at all, on threat of losing the payment services.
Crypto cash and gift-cards are great if you have effective access to them.
It's not that people find cash less convenient because they are lazy (some are i suppose), it's because it's being purposely deprecated as much as possible, or just straight up doesn't apply to the paradigm, such as online purchases.
As i said, this already happens, it's weird in how it's applied tbh, but that's neither here nor there.
https://www.adyen.com/legal/list-restricted-prohibited
Mastercard just says : "brand-damaging Transactions" and doesn't elaborate, at a quick glance.
A good example of this is casino's and other gambling related physical locations, there are a lot of hoops to jump through to get a payment processor to work with gambling, assuming they even give you the time of day.
Sure for that specific thing, hard to pay cash at amazon or other online only retailers.
That i'd be interested to see tbh, because as i said there isn't an equally available alternative to card payment processors (and it's not even close).
If they did go crypto only for instance, there'd be a big move to crypto for some, but that'd be a significant loss to take on principle alone.