Criticism is good, and users should point out the flaws in their OS of choice. Regarding the FOSS vs. proprietary/closed-source debate, it is one of ideology and very like religion, political party, etc., so either side will believe their choice correct and the other's wrong.
I will note, though, that there is a scale of freedom in FOSS licences, the GPL being, for example, much more restrictive than the permissive MIT. Many projects avoid or can't use GPL code because of the control or implications it entails. Ironically, we have a number of Windows components under MIT, meaning people can do what they want with it.