@georgia If one package is proprietary, that's not a problem, as well you just delete the package and then the OS is free.
But it's never just one - as soon as the evil sort manage to get one proprietary program in the door, they don't stop - they keep adding more and more, until you've ended up with a kernel that is >51% proprietary software and an OS with so much proprietary software, that the amount of proprietary software seems to dwarf the amount of free software.