As a general rule, I believe that knowledge is free. Anyone can pick up a book or surf the internet and learn. This isn't a recent change; it's been true for as long as there have been public libraries.
So when Richard Stallman came around the University of Saskatchewan in the early 1980's, preaching the gospel of the GPL (GNU General Public License) and LGPL (Lesser or Library GNU General Public License), he found a host of interested ears in the university student population. Many an hour were spent debating the merits of the GPL and LGPL and the edification of common knowledge.
Remember, while we had email capabilities back then, we really didn't have an internet yet. We couldn't envision any way of sharing code other than to post updates regularly for download from the news feeds, or to find someone with an FTP server we could use to host tarballs.
We all understood what we wanted to do -- build a knowledge space dedicated to the principle that the knowledge itself should be free to all, especially the code that is used to build the space. Digital Space must remain free if all of humanity is to benefit as it should.
In the purest sense, the GPL was anarchy from the rebellious university youth. Who knew so many of us would turn out to be successful career programmers with influence on the business environment far beyond our individuality?
Open source has taken over the majority of the computing world. I firmly believe that it's inevitable for this to happen, because those willing to contribute their knowledge to the knowledge pool are a steady trickle of drops downwards. Each drop is small, but look at the size of the ocean they splash into and build!