The goal as always is to divert my attention, sell me something of dubious value or some other equally vacuous purpose.
If it pays the bills for worthwhile content producers to mine crypto currency as a form of micropayment, I think that's a better trade with lower psychic cost.
I have managed to make periods in my life completely free from unwanted content, and they are blissful compared to the never ending attention grabbing bs of the advertising and public relations engines of modern industry.
They are simply a waste of people's time and energy.
If crypto-mining is done openly, of course. It's certainly dishonest if it's not disclosed.
Also, I’m conceiving of this more as a web API browsers can implement that sites can tap into than as a chunk of JavaScript that a site pushes to its users. So, arguably, you’d have consented to this scheme by installing the browser and enabling the feature.
Indeed, such behavior is reminiscent of one of the oldest tourist scams in the book, no doubt experienced by anyone who has traveled the world in any amount.
That is to say, the mark is offered something for free, usually some trivial trinket, or a photo, or something like that. The mark believes it is for free and accepts it. Once the mark has accepted the "free" item, then the scammer changes tune and implies that they should be paid for this exchange, playing on the marks feelings of guilt, obligations and fairness.
Apparently this is now a respectable internet business model. Hah!
Honesty breeds honesty. I disable ad blocking on sites that ask nicely and don't spam with ads too much.
[1] I'd be OK with it if they prominently indicated that, how and why they were being electricity vampires. I still wouldn't use them, but at least it wouldn't be dishonest.