Well OpenAI is consitent in that it consistently tries to monetise other people's work without paying for it and in doing so it leverages the gullibility of the masses to defend their actions. Clever.

An artist using an artbook as reference material = good

An artist tracing an image in an artbook and selling it = bad

Seems consistent to me

I think it's worth reframing this analogy:

An artist using an artbook as reference material = good

An artist with one billion arms, using every artbook ever published, creating millions of images per second in every possible style for fractions of a penny per image, outcompeting every other artist forever = bad

I think I'm sympathetic to that idea, but the ethical consideration there isn't that it violates copyright. It's that it's disruptive to society/the economy.

Or maybe one could argue that because it's owned?

Art books are not free, they require paying a licensing fee to the rights holder.

If the artist stole the artbook from a shop, the problem is not that they are using it as a reference; the problem is that they stole it. Likewise if they download the pdf from a pirate site. It is a separate, different problem. You can tell because there would still be a problem even if they didn't then go on to produce art, or read it at all.

If, however, the rights holder chooses to just give them away; or, y'know, puts them on their own website for anyone to look at - there is then no license fee to be paid for looking.

Note that this still does not mean someone can make copies and sell them. That's a separate right. But using such materials as a reference is just fine, and people do this all the time.