You can absolutely take things from a house with an unlocked front door, if there's no jail time and the fine is one [insert local unit of currency here] and that theft doesn't hurt your reputation. That's how AI works right now:

"No one sued us before we made it to market with our models trained on stolen property, and now we're entrenched with a billion dollars of legal defense funds and budgeted for the fines in case we end up convicted of robbing you — and now our customers pay us to externalize and disregard the robberies we committed to reduce their effort, so they have the moral high ground and we wallow in our wealth."

>"No one sued us before we made it to market with our models trained on stolen property, and now we're entrenched with a billion dollars of legal defense funds and budgeted for the fines in case we end up convicted of robbing you — and now our customers pay us to externalize and disregard the robberies we committed to reduce their effort, so they have the moral high ground and we wallow in our wealth."

What about "all art is derivative to some extent, and training a machine artist based on existing art is no different than training a machine artist based on existing art"?

Then the Stable Diffusion model should hold the copyright. And using generative models doesn't make you any more of an artist that commissioning a human does.

That is for the courts and the lawmakers to decide, and in any case I don’t plan on convincing anyone to change their mind about ML training ethics.

It can be how the law works; like in Field v. Google Inc. for hosting a cached copy of a site: "Google reasonably interpreted absence of meta-tags as permission to present "Cached" links to the pages of Field's site".

I think Fair Use is the stronger defense for model training, but - for crawlers that obey robots.txt/etc. - implied license isn't totally off the table.

That's a pretty poor analogy. To make it a bit better, it's also like we're figuring out what this whole "house" thing is, and there's lots of differing opinions, and also lots of people who think this whole "house" thing is a fad.