"I honestly don't think it's simple. How can I possibly use GPL code to reduce anyone's freedom? By creating some derivative work? By doing so, I have not diminished your access to anything that already exists!"
Suppose you were a farmer that left town for a week or two. In that time I came in, fed your chickens and then took all the resulting eggs.
How can the above be theft? I haven't diminished your access to anything you already owned!