Proprietary software is not illegitimate, just problematic from the economic sense. Open Source software gives many advantages to the end-users and is a generally a good thing. Copyleft licences may be important in making sure certain software is not abused. (Note, however that even Raymond recently voiced his opinion that the GPL is no longer a wise choice as licence for new code). It is not immoral to use proprietary software, it’s just risky. Using or producing software that is not 100% open-source but pretty close, can be a good idea, depending on its licence and the general attitude of its developers.