Much like how some artists are uncomfortable with making high-quality scans of their work available online, because it becomes prohibitively difficult to prevent people from selling prints. Forget the current legal framework, it seems fair to me to say "I don't want that happening to my art" when "that" is a corporation finding a way to monetize it. Even if the AI is using less than a pixel of your work, I think it's fair to ask that it not.