Intent (should) be what matters. If you want to learn how to train AI and use copyrighted material in your learning - I don’t care in the slightest at all.

In fact if you do this as a nonprofit or at an educational institution in a teaching context it’s explicitly allowed by fair use already.

If you do it individually, idk I’m not a lawyer. But it should be allowed on principle.

But if you then go take your trained AI and deploy it for commercial purposes that’s a different story and should have protections for the original rights holders.