So, to be clear, your argument is that the freedom to deny the freedom of other people is a freedom that should be protected? How do you deal with issues like slavery and, in particular, its abolishment?
usea's argument is clearly not that but only that you can't literally think something is "not worth discussing" while you are actually discussing it.
The person who was explicitly defending non-GPL licences was rahkiin. I don't know how they'd respond to your challenge, but here is how I would:
"The freedom to deny the freedom of other people" is impossibly vague, because "the freedom of other people" can mean zillions of things. It's also confusing to talk about since we have two separate freedoms here, so let's talk about the freedom(1) to deny the freedom(2) of other people.
Suppose we put "the freedom to kill other people" in the freedom(2) slot. Most of us think that isn't a freedom people are entitled to, so the freedom(1) to deny that particular freedom(2) would be a good thing.
Suppose we put "the freedom to breathe the air" in the freedom(2) slot. Most of us think that is a freedom people are entitled to, so the freedom(1) to deny that particular freedom(2) would be a bad thing.
In the present case, what goes in the freedom(2) slot is something more complicated and less clear-cut -- it isn't a Super-Obvious Fundamental Human Right like the right to go on breathing, but it also isn't a Right To Do Very Evil Things like the right to murder.
It's something like "the freedom to read and modify the source code of a particular piece of software". We demonstrably don't presently have that freedom as regards many widely-used pieces of software; the world's legal systems pretty much unanimously agree that if you put this in the freedom(2) slot then the freedom(1) to deny it is worth having.
Why? Well, the usual arguments would be (1) that creating something gives you some rights to limit what other people do with it, and (2) that giving creators some such rights is a good thing overall because it increases the incentives for people to create nice things.
Of course you might disagree! (And, also of course, even if you agree with #1 and #2 in the abstract you might think that "intellectual property" law as currently implemented across the world is a very bad way to get #1 and #2.) But I hope your reasons are a matter of thinking carefully about the tradeoffs involved, not just of saying "yay freedom" and therefore denying every instance of "it's good for X to have the freedom(1) to deny Y's freedom(2) to do Z".
Not least because you literally can't consistently do so in every case -- if you say no one should ever have the freedom(1) to deny freedom(2) to others, whatever specific freedom(2) may be, then what you are calling for is precisely to deny that freedom(1) to others.
If that was true, you wouldn't be doing just that.