You're reading a lot into my reply. The GP's question was "is there any better way to [avoid the captcha] with a single developer?".

That's clearly the case. As a trivial example, 4chan could take your $20 and avoid giving you a captcha for 2 years, or charge you $10 for one year.

Both are a 2x improvement, if the only goal is to get past the necessary evil of the captcha.

But that clearly isn't the goal, that doesn't mean I'm begrudging 4chan their business model, that's something you grabbed out of thin air.

    why would they not kick the
    problematic and porn boards
    to the curb and ban the use
    of slurs to make room for more
    friendly advertisers?

How would that be a realistic alternative for the "single developer "? The entire selling point of 4chan is that it's a very limited time capsule of the old Internet wild west.

What you're describing would be a Reddit or Facebook groups clone. If 4chan became that, nobody would use it. They'd just use Reddit or Facebook groups.

Cynical yes, incorrect no.

The link between spam protection and payment is well documented and as old as the internet.

Consider the origins of bitcoin and PoW have been as a currency to stop email spam.

I do agree that the incentive is probably not to make money, but to deter spam. That said after so many times the company has been sold, I wouldn't disregard that theory

Doing so would destroy the culture of 4chan.

Companies centered around communities don't generally have leeway to shape their communities into a profitable form by directly altering the fabric of the community. Time and again it has been shown that forcing changes to the identity of a space leads to communities' rapid demise. In rare circumstances and with a skilled hand a community can be guided here and there in even some significant ways, but 4chan probably does not have that option: they'd need a massive shift to pull off what you describe.

Instead profit must generally be built around what is there. But whether or not such communities exist to make profit, they surely must be profitable, or they will not survive. They must, some time or another, be free of deficit. This is not a matter of capitalist greed for most communities, but an attempt to find a path towards stability.