So you're using the world "developer" not as the one creating the project, but as the one retrieving it and modifying it. That's actually what licenses call "us

So you're using the world "developer" not as the one creating the project, but as the one retrieving it and modifying it. That's actually what licenses call "users", and copyleft licenses improve your liberties by maximizing the amount of projects that are Free. What copyleft licenses prohibit is distributing software with less freedom than what you had when you received it, whether you modified it or not. But that's not a developer's issue, that's an issue for someone that hopes to gain something from restricting freedom.