Free Software Foundation was created to fight all and every form of proprietary software. For the philosophy of free software and the FSF society should be 100% running on free software, because proprietary software is seen as a non justified mean of control that the developers can use against the users.
Proprietary software: the devs has ultimate contol over the software (both on a theoretical level and practical level)
Free software: the users have control over the software, at every moment they can decide to take the source code read it, do modifications, and share modified copies with others.
And there is no other way around it, either the software respect the user's freedom or there is an unjustified means of power that cannot exist.
The same exact way we cannot give full powers to a politician we cannot give one entity (be it a company or a single dev ) full power on how software works, since our entire society today is digital and freedom is required in the digital space too.
The only way to reach this is not having the dynamic of power that proprietary software gives terracore to it's devs.
This is just a part of my thought on free software.