Earlier quoted context omitted.
Do you know that according to copy rights, open source projects are mess. Nobody tried it in the court, but if some developer contributing to project went to court saying "This part of code is mine, I don't want it to be modified by other people", then the project could be in trouble. Nobody tried that (yet). That's why some OS projects require signing Developer Certificates of Origin etc.
What I meant here, is not that GPL was not tested in court. Just imagine situation of one of the authors saying: I no longer want to see my code on the Internet. Let's say he contributed 30% of the code. Now what? He is the author, he has the right to do it. In most cases developers sign no agreements when their patches are merged.
The world would be a much different place if smart people in the past hadn't invented Copyright and Patenting, which both are mostly being misused and are not used to foster innovation. Back then it was normal to hold onto secrets and patents and copyright were invented to incentivize publication under well-defined and not too long exclusivity periods after which other can freely improve on it. But today we have 20 year patent monopolies and Disney copyright absurdity.