Which of the four freedoms (ignoring that only freedom #0 and #2 apply to users) is violated by using more liberal licenses like MIT or CC0? Freedom #0 is clearly violated by GPL projects: GCC for years tried to be prevent to be run as a library or in combination with other programs. Running ZFS or the better proprietary graphics drivers on Linux is a bit questionable legally.
GPL being incompatible with app store rules kind of breaks freedom #2 and #3.
> Which of the four freedoms [...] is violated by using more liberal licenses [...]?
None of them [which, as you probably know, goes without saying because they're both free software licenses]. The problem is that a project using a lax/pushover license is that the project can be used as a tool for violating user freedom. For examples of this, see the PlayStation and other such products which were developed thanks to the existence of free software under lax/pushover licenses.
As an aside, the thing that personally made me care about the prolonged effects of copyleft is that I realised that if I wanted to contribute to a world without proprietary software, every non-copylefted program that I wrote was potentially acting against my intentions. You might not see it that way (and I didn't see it that way for a long time), but that's why I made my decision.
> Freedom #0 is clearly violated by GPL projects: GCC for years tried to be prevent to be run as a library or in combination with other programs.
That is simply not true, and is a non-sequitur to boot. It _is_ true that the GNU project decided to make it hard to create proprietary modules [or otherwise external modules] for GCC, but nothing stopped a user [in principle] from doing either of those things. The GPL doesn't require a project to make themselves usable as a library.
> GPL being incompatible with app store rules kind of breaks freedom #2 and #3.
But "app stores" are acting against user freedoms, which is why you can't distribute GPLv3 software [without additional permissions] in most "app stores".
In fact, I would argue the GPL is doing its job well here. It's preventing the re-distribution of free software in a way that harms user freedoms. That's sort of the whole point. Just because you don't care about how "app stores" treat users doesn't justify claiming that copyleft is acting against users here...
