I get that the concept is upsetting. And, I'm not going to tell people to not be upset or not state their will. Ex: DeviantArt has instated an opt-in checkbox for "It's OK to train on my art" and I think that's great.

But, everything I've heard and learned about how AI works leads me to the conclusion that such a move is almost entirely symbolic. Counter to what our egos would like to believe, the vast majority of the training images and the vast majority of the learning value for AI comes from random, crappy photographs of various things. Without a million photos of dogs and trees, the AI can't make a stylized dog distinguishable from a stylized tree. And, it's turning out that, from that base of crappy photographs, it doesn't take many high-aesthetic images to make a high-aesthetic AI.