There are also many reasonable ways for closed source software (or more accurately "non-free proprietary software") to make the sources available for review, but not give away all the rights. Like "Microsoft Shared Source Common Language Infrastructure", etc.

Of course it's better for software to be free / open source, but it's nonsense to imply that only open source software has the potential to be seen by "many eyes".

My eyes are still red and sore from staring at the MFC source code before the turn of the century.