This topic comes up again in another thread. But I'll answer the question. Absolutely unimpeachably ethical. It is absolutely ethical to use the work of artists, even without their direct approval, to train AI.
When defenders of "copyright" (a false term) come forward, the following picture is presented: crowds of wild people communicating with gestures and unintelligible sounds. And then comes the Author. He invented words, letters, notes, music and color theory, composition and other things that make up not only art, but also just communication between people. Yes, in such a case Copyright is in place, has the right to exist and requires full remuneration. But it simply cannot be so — all works are compilation and synthesis of all previous experience and findings of development of society and civilization.
Here is an artistic photograph. Does the author of the photograph remunerate the inventor of the camera, the creators of the camera, the people in the picture? And if the photo is of a building: a house or a bridge — do the builders and architect (or their heirs) receive royalties?
If the Creator uses, for example, a Biblical story in a work, then he should pay royalties to the creators of the Bible (or their heirs).
Stealing (plagiarism) — when works are directly passed off as one's own. There is nothing completely original in any work of art. All subjects are known — only a slightly unusual interpretation and reading is possible. Using known artistic theories. Even new theories are only possible on the basis of old ones.
Yes, when teaching AI, all artistic works should be considered public domain a priori.
Copyright. (Author's rights) Let's be honest. A situation where the creator directly receives royalties is extremely rare. Mostly it is not the creators who receive income, but the copyright holders. This is a big difference. The owners of the rights — publishing labels — have enormous opportunities to put pressure on authors and get the rights from them, not excluding direct crime. The presumption of guilt should work against corporations, and copyright should become inalienable. Only then we can begin to talk about the shadow of fairness in relation to royalties. It is for this reason that the term is false by definition.
The income of AI developers. What is this even about? AI development is an extremely costly endeavor: expensive specialists, valuable equipment, dead-end but resource-eating paths. Chinese AI turned out to be relatively cheap for the reason that the Chinese were already following the beaten path. And AI training itself is not a cheap process at all. In this situation, even to recoup the invested funds seems to be an extremely long and difficult task. And access to AI can often be obtained for free, albeit in a limited amount. There is still a long way to go before profitability.
And heirs of those who had something to do with artistic creations (models in paintings, builders and architects whose buildings are depicted or mentioned in works, heroes and participants of biblical stories) can get access to AI for free. Which is fair.
On the subject of copyrights it is very useful to recall the story of Aaron Swartz. May I not give the link — educated, cultured people should know it.