MTG

Plagiarism is taking someone's ideas without proper credit

Plagiarism is not merely the act of being inspired by another source. It's passing off someone else's work directly as your own. Derivative work is not plagarism, you don't even have to credit for that so long as it's transformative enough, which is where it intersects with copyright law. If I see a cool piece of art and am inspired to draw something in the same style, that's not plagiarism by itself unless it is essentially a draw-over or directly copy-pasting their work.

1. A passage or thought thus stolen.
2. The act of plagiarizing: the copying of another person's ideas, text, or other creative work, and presenting it as one's own, especially without permission.
3. Taking someone's words or ideas as if they were your own.

American Heritage Dictionary 5th edition

1. to steal and pass off (the ideas or words of another) as one's own

Merriam Webster

1. the process or practice of using another person's ideas or work and pretending that it is your own

Cambridge Dictionary

You're free to not like AI art, but it's not plagiarism to train the models. It's not plagiarism to use the models to generate new art. I'm not plagiarizing the thousands of pieces of art I've personally seen if I draw something new by myself. If an artist paints something new, do they need to source every single piece of art they've seen in their lives? They've been influenced by them all and they all collectively contribute to the ideas that artist comes up with, so why not? Where's the line?

Now, if you're going out and claiming the art as your own then I personally believe that could absolutely be considered a form of plagiarism since technically it was the model doing all the work, but it's certainly not plagiarizing the millions of pieces of art it was trained on. Those art pieces are not copied or directly reused in the model's memory, it uses the general structure and form of the artwork to create new works.

Copyright infringement is also iffy since it is very likely to be considered transformative and therefore permissable under fair use.

Again, you're free to not like how the models are trained, but calling it plagiarism is just flat wrong.