Eventually all software should be open-source from the mere reason that software writing is a form of Art, & it's wrong to hide art in private places.
The art is in the concept, architecture, design & algorithms.
Though people tend to think in economic models, what actually drives the world forward is the advance in art: seeing the world differently & the implied ideas & thoughts.
"Art is the greatest riddle, but man is the solution." (Joseph Beuys)
Of course, there are other reasons for Open-Source, such as the need for transparency in the (information) machines (code) that control our life, as recently discussed in Muli's blog.