I haven't "redefined" it, I'm using the legal definition. People do sometimes sloppily equate copyright violation with theft in common parlance, but they're in for a rude awakening if they intend to try translating that into legal action.

Using that term in an argument like this is merely trying to beg the question of whether it's wrong, since most everyone agrees that stealing is wrong you're trying to cast the action of training an AI as something everyone will by default agree is wrong. But it's not stealing, no matter how much you want it to be, and I'm calling that rhetorical trick out here.

If you want to argue that it's wrong you need to argue against the actual process that's happening, not some magical scenario where the AI trainers are somehow literally robbing people.