Completely depends on how much you've "mixed in", and facts specific to that individual work. Fair use doesn't get thrown out the window because GPL authors ha

Completely depends on how much you've "mixed in", and facts specific to that individual work. Fair use doesn't get thrown out the window because GPL authors have a certain worldview. Second, there are a lot of non-copyrightable components to source code - if you can't copyright it - you certainly can't GPL it. These can be copied freely by anyone at any time.