That would, I suspect, be the point. If your AI is trained on non-free content, the implication is that it would be impossible for it to be released with an op

That would, I suspect, be the point. If your AI is trained on non-free content, the implication is that it would be impossible for it to be released with an open source licence. So don't do that, the argument goes: only use content that has been released with a sufficiently free licence that republishing it in your dataset is not a problem. And as a side effect, you have to show that there isn't any "misappropriated" content in your training set. That side effect is what gets some people excited here. I don't agree with that position legally, but I do mechanically. The point of the GPL family (to pick one random type of licence) is that the end user should have the capability to modify the product to their own ends, and I don't think fine-tuning provides enough capability to qualify.