The "nothing of value was lost when you pirate" argument. I'm a game developer who fully encourages people to pirate my games (or email me if they can't afford my games and want a free Steam key) but I can tell you value is lost when people pirate content. Even if that's simply a positive Steam review which in turn will put you higher up on placements on Steam's algorithm which will gain you more sales. Something of value is lost when you pirate. It's on the artist to determine if that value is acceptable to be lost. If they made their art for the sake of humanity or if they made art for the sake of survival in our shitty capitalistic society.

So sorry, yes, something is lost and it's because of capitalism. I'd argue otherwise if it didn't mean someone didn't get to eat or pay rent. I pirated a lot of media back in my day when I couldn't afford that media. I used to tell myself I wouldn't have likely bought those things anyways. That I wasn't taking from someone. In reality, I would have waited for a sale and gotten that media for 5 dollars. 5 dollars is still a lot of money when selling something though. If I just gave you 5 dollars you could do something small but nice for yourself. You could go buy a lot of things with that sale money. Just because you aren't spending 60 dollars on it doesn't mean you would never buy it. The fact that you want to play it says you'd probably buy it. Maybe you'd refund it. Maybe you wouldn't. Your time is worth something to you though. Thus when you pirate something you are committing something of value from yourself to search, download and ingest that media.

So how does this deal with copyright theft? Stealing something and using it devalues the original product. You've seen it a dozen times for better or worse. Minecraft is a great example of how it got devalued for a while there when everyone made Minecraft clones. My kid told me the other day that he got Minecraft on his tablet for free. It was some terrible knockoff he had been playing. I explained this and asked if he wanted the real thing. He said yes and I went and bought Minecraft. That in itself is proof that value is being lost by even legally taking an idea and copying it. A kid's parent who didn't know better would have just been like "Hmm, that's great, have fun." The best point I can make is that if there was one video game ever, to play a video game you would have to buy that one game. That one game would have more sales than any single game out there today. Clearly, something of value is being created by the exclusivity of copyright.

There is, of course, a balance. What is copyrightable? What stifles creativity and innovation? I would say if these AI artists were able to recreate the style from prompts and only train the AI on images that it has the authority to distribute (public domain images, CC0, etc.) then it's fair game. Training AI on copyrighted materials and then distributing derived works is copyright theft and should be deemed as such.

Copying art for personal, non-commercial use is not theft, but copying someone's art and then profiting (using their image without permission to enrich yourself) is theft.

"Is copyright infringement theft" is something that had been debated for as long as mp3s were a thing. This is an old argument with lots of material on both sides scattered across the web. I clearly fall on the side of copyright infringement is theft and theft is stealing.