Earlier quoted context omitted.
There is another option. CAPTCHA is useful only when it is costly to solve. It is a costly signal that this is a real person, or at least is more than 1/10^9th of a real person (you're not running a fully automated spam system). The postal service also has costs - everybody that wants to move something through the postal service needs to buy a stamp. Transport fees are a 'natural' way to moderate traffic and deter sp…
If you expect 99% of normal internet users to maintain a crypto wallet of any kind just to access certain websites—even leaving aside the actual cost—you're going to be sorely disappointed.
the only way this makes sense is you convert the entire planet to renewable or non-polluting electricity generation, and then when a user is on facebook, youtube, (or watch ads!), a core or 2 of their machine/phone will "mine" crypto, that can then be used somewhere else. The crypto can't be transferable - it must be "burned". Defined: When the site requests some crypto for proof, it says "send to this non-existent address" and then waits for the block to show that your wallet sent crypto to that address. This "burns" the money. In fact, a couple of cryptocurrencies tried to enforce this, as well as "proof of stake" - where if you had enough coins you could "mine" by merely having your wallet "logged in." The former is called "proof of burn"
another thing, no blockchain block publication is fast enough for this. so now we gotta rope in lightning or some other "hack" on top. I knew when i first heard about bitcoin that there was no way that anyone was going to wait 10 minutes for any payment to go through, especially if it's under some moderate amount of money, like $20.