You fail to understand how copyleft works. The whole point of licenses such as GPL for example isn't to allow the user to do anything with the code. Doing so would allow ruthless businesses to immediately take advantage of that uncontrolled freedom because all patches, forks and derivative works would become closed in no time. The point of such licenses is rather to give more freedom to the majority of users by preventing others from restricting how software would be distributed.

> This is the true spirit of free and open source software. Sharing code with the world for the collective improvement of software everywhere.

Did whoever took your code share their bug fixes and updates with the community, so that the original code could be improved? If not, that would actually be against the true spirit of free and open source software.