Available for free online is not a valid justification for copying under copyright law, though, right? You can’t distribute something just because you can see it. True for museums and magazines as it is for online content.
> They don’t have the right to not allow people to learn from it, that’s just never been a part of copyright.
Yeah this is true. Stable Diffusion and other neural networks are not “learning” from it they way humans do though, it’s remembering and remixing and interpolating pixels (fixed expression), which is a part of copyright.
BTW compensation is not a very accurate summary of this problem. Machines that borrow someone’s style and copies and remixes without attribution is inherently problematic far beyond artists who live off selling their art, it dilutes both creativity and credit, in addition to undermining people who have to work much harder than the computer to produce images. These AI completely depend on being given human-created art to begin with, and the companies that are making them and using them are already making handsome profits, so it’s reasonable to expect some kind of return in addition to proper credit.