I think I'm starting to understand... If I go to an art gallery that allows photos, take some photos, and share them with a friend who is learning to be an artist, that seems to be generally ok and does not feel unethical. But if I take those photos to an underground sweatshop and use it to train a thousand people who are mass producing art for corporate use, that seems wrong.
If I think of the AI as a human analog, then I have trouble seeing the problem with it learning from the same resources as humans, but if I see it as a factory then I see the problem.
We need better solutions for proving identity online. Email, capcha, etc. are insufficient. I imagine a system similar to the certificate authority system, where you prove your identity to one of many trusted identity providers and then that provider vouches for you when you sign up for other services (while also protecting you anonymity.)