They would need to figure out a way to prune the respective weights so that such material is not available, or risk legal fury.
Youtube doesn't need to figure out how to stop copyright material from being uploaded, they need to stop it from being shared.
You want to reliably train it away from outputting the undesired outputs, not keeping it ignorant about them.
They would need to figure out a way to prune the respective weights so that such material is not available, or risk legal fury.