Please explain why you cannot download a movie/episode/ebook illegally and then directly derive from it.
The law does not prohibit the receiving of an unauthorized copy. The law prohibits the distribution of the unauthorized copy. It is possible to send/transmit/upload a movie/episode/ebook illegally, but the act of receiving/downloading that unauthorized copy is not prohibited and not illegal.
You can’t illegally download a movie/episode/ebook for the same reason that you can’t illegally park your car in your own garage: there is no law making it illegal.
Even if ChatGPT possesses an unauthorized copy of the work, it would only violate copyright law if it created and distributed a new copy of that work. A summary of the work would be considered a “transformative derivation”, and would fall well within the boundaries of fair-use.