Most of the lefties I know value government control/planning. OSS is, arguably, uncontrolled and unplanned. Anyone can start an OSS project. Anyone can contribute. No one's approval or permission is required. You could argue that OSS is freer than closed source commercial development projects (if I'm paying the bills, I call the tune). The freedom available (not necessarily taken) to the individual via OSS is surely anathema to lefties everywhere.