Excellent points mjburgess!

>I think the blockchain as a deliberately computationally expensive ledger is an interesting idea, and at least a plausible account of what resource could count as a commodity.

That's exactly the idea.

>It is certainly why BTC tends to have a implied floor around cost-to-mint; but that is more the psychology of its use. It's floor is zero, as with anything: whilst a token on a blockchain has no productive value below its (energy) cost-to-mint, that doesnt create buyers at any positive price.

Yep, that's exactly it. BTC however has huge transaction fees which limits it's applicability as a spam prevention tool. Small comments in Quora, or Twitter cannot be annotated with 10 cents of a transaction fee, it is too expensive.

>One issue is that I don't see deliberately making computation less efficient as something unique to blockchains: we can make present systems abitarily energy-intensive by adding hash-computation work to them. We dont need immutability and distribution to do that.

At first glance, yes, we can create intentionally expensive computations without relying on a blockchain, that would serve the same purpose. In reality we cannot. Special computer hardware (ASICs) could generate much cheaper PoW annotations than general purpose computers, and sell it to spammers. Blockchain economic incentives ensure that ASICs will be used by the miners first and foremost.

That one point is exactly the genius of Bitcoin. The competitive system of blockchain miners, ensures that over time the best hardware and programmers to create the most efficient PoW, will be bought/hired by the miners first.

>However, I'm not sure in a world wish such high negative externalities on energy consumption, selling deliberately high energy cost computation is plausible. Unless spam can be shown to have similar externalities, as a problem, it's vastly less significant than our global energy crisis.

That's a valid concern. However energy, and electricity more specifically, is dirt cheap and abundant in many places of the world, in which no human lives in a 100 mile radius. Solar panels in the middle of a desert for example. Time of the day plays a role as well. A significant amount of energy is wasted, just because humans don't consume that much energy, that time of the day.

>Services which perform computation to reduce spam, almost certainly, perform far less than the blockchain alternative. Minting a coin for each YT video uploaded is a vastly inferior solution than: 1) YT charging for posting videos; 2) YT building & running anti-spam systems; 3) YT charging users for access to videos; 4) YT requiring users having to hash something before uploading, so costing them some energy, etc.

Well, YT the video service could charge for every video uploaded less than a cent, let's say 0.1 or 0.01 dollars in Bitcoin, not BTC. Most video creators couldn't care less, if they pay 0.1 cent per video. Spammers however care a lot. In case someone uploads millions of videos, money suddenly start to add up. Tens of thousand of dollars for a spammer to pay, means he will stop spamming soon. Different charging methods could be implemented as well. Maybe charging a dollar for every 100MB of video is preferable. Charging methods could vary a lot. Reputation lists and trees, could create different charging methods as well.
Relevant: https://www.youtube.com/watch?v=Olkb7fYSyiI