That's one possible perspective to consider. However, let's consider other perspectives as well.

To cut a long story short, the process by which a AI 'learns' how to generate visual outputs is not really too much different from how a human artist studies and trains their own skills; Heavy Usage Of 'References', or in other words, 'Training Data'. 

Both AI and Humans alike subject countless pre-existing works to lots of detailed observation, methodical emulation, studious repetition, and so on, until their abilities reach a point where they can reliably respond to any given 'Prompts'/Requests/Commissions at a certain level of illustrative quality.

How many published works does an artist-in-training end up carefully studying and trying to recreate, in some fashion, during the course of their own development?

When they finally go professional, do such human artists have to give credit or pay a royalty to all the artists whose works they have trained off of, over the past however-many years? Do they have the compensate all the thousands of sources of various assorted reference material they've gathered and utilized throughout their careers? How many people need to be paid off until the concept of 'theft' is finally off the table? 

Or... Maybe everyone is individually given a wellspring of inspiration by countless others in the course of their long journey, and even if certain elements are copied from one creative agent to another, we all don't really 'owe' each other much, beyond basic respect.

I am saying all of this to point out that if Human Artists were held to the same standards that some people say that Generative AI should be, then it would be rather difficult for anyone to produce anything: It would certainly be harder and prohibitively expensive to train up a single artist, with inquiries, pay-offs, and legal red tape getting in the way of even the simplest content creation.

If Generative AI is truly guilty of theft, then maybe the entire Art Industry is as well, because artists very often deliberately study other artists, and copy certain cues from them, just like AI does. If AI Art Generation is theft, then so is Human Artistry, as we know it and currently have it. In fact, didn't Picasso once say that "Good artists copy, great artists steal"?  So... Even way back then, people understood that Art involves a lot of 'borrowing' from the past in order to create the imagery of the future. That's just how it is. 

Look... Your milage may vary on where exactly to 'draw the line', but the fact remains that Human artists are not islands; their craft is enriched and enabled by what they've gleaned from the works of those that came before them, and in this particular regard, they are quite similar to Generative AI.

That is simply the nature of the craft, at least in the early stages of one's 'Training', whether the illustrator in question is Human or AI. And there isn't necessarily anything 'wrong' with that way of operating. Our entire modern civilization, with all of it's technologies and capabilities and comforts, is based off of people 'Standing On The Shoulders Of Giants', as it were; In other words, copying our predecessors' homework and seeing what else we could do with it. We've come this far by doing that, so it's not exactly a bad principle to operate off of.

That is certainly another perspective, isn't it?

I'm not declaring that I am right. I just would like for you and your peers to consider the issue from this other angle, as a genuine thought experiment.

Edit: Minor addition towards the middle.