If you want to keep your code closed, then you're more than welcome to do that. Just honor the choice that others have made with their code.
This limit is perfectly in line with the Declaration of the Rights of Man and of the Citizen. I argue that anything that allow this limit to be crossed does not most efficiently promotes freedom.
Yes, permissive licences do not most efficiently promote freedom. (Don't get me wrong: they do promote freedom.)
Now the AGPL, because of its additional restriction, could be seen as less free. I think that technically, it is (it doesn't fully give you the right to private modifications). But the spirit is the same, applied to remote applications instead of distributed software.
[Condescending explanation] Among the four freedom, free software gives you freedom 1: the right to private modifications. Meaning, as long as you do not redistribute the software, you don't have to redistribute the source code. And if you do distribute a particular version of that software, only that version of the source code must be accessible. You can still conceal a private fork.
Now in the case of software executed remotely, or software as a service, Eben Moglen himself reckons there is a conflict of rights: because the client is effectively using the code, it should have access to the source code. And because the server do not actually distribute the software, it should have the right not to release anything.
You can't satisfy both rights at the same time. The GPL satisfies one (it is 100% compatible with privacy rights), and the AGPL satisfies the other (and makes itself incompatible with some privacy rights in the process). That's a pity, because before the rise of software as a service, the GPL was the ultimate freedom respecting licence. Now you have to choose between two compromises.
PS: Don't say "property" about software, if you can help it. It is a inaccurate analogy from the physical goods, which fail to convey the truth about knowledge. (Of course, software is pure knowledge.)
Specifically, I'm skeptical of the claim that if a client uses code, he or she deserves access to the source code. Sure, it's probably better to provide access to it, just like it's probably better to donate to charity, but I don't think either should be enforced by threat of violence (while it may sound silly initially, software license litigation boils down to a threat of violence).
To me, code in the public domain (or all code in a society with no legal protection for code) is perfect. That seems to me like purer freedom.
Lastly, when did I say "property" about software? I'm against legal protection for intellectual property when it comes to software. I agree that software is pure knowledge, every piece of software (that compiles/runs) is an algorithm (in fact, a number), and that writing a piece of software or coming up with an algorithm should give you no inherent ownership of it.
What you call "purer freedom" is actually negative freedom, which is about not forbidding. The GPL promotes positive freedom, which is about enabling. As we can see when we compare the GPL and permissive licences, the GPL is more effective at enabling everyone to look at the source code. For me, that's what counts. I don't care about how "pure" the freedom is, I just care about it's effectiveness.
Lastly, you said "Free software […] is incompatible with privacy and property rights". "Privacy" was appropriately used, but I think you tossed "property" without much thought, using its positive and undeniable aura.
How can this be a negative vs. positive freedom argument? Not distributing source code places restriction on the client, while forcing developers to distribute source code places restriction on the developers. Either way, if software usage is restricted at all, then someone's freedoms are going to be restricted. The only solution I see is for there to be no legal protection of software, period.
I used "property" to refer to the physical hard drive holding your data, as well as your house and land. Of course, many argue that privacy rights follow logically from property rights, so the distinction probably isn't necessary.
To exercise your right to free speech, the only reasonable way is to use the Internet. And you need to run computer code to do that. Similarly, to protect your privacy, the code you run (all of it) has to be trustworthy. And I say that to be trustworthy, the code must be free, at least for you. Conclusion: running free code (and only free code) is necessary to exercise some fundamental rights. Therefore, everyone deserve it.
The positive/negative freedom argument comes from the facts that (0) the four freedom are way more important than the freedom to proprietarize software, and (1) they conflict. If you want to preserve the greater freedoms, you have to sacrifice the lesser one. Now, people could be reasonable, and respect the four freedom even when they are allowed not to. But I think we can agree that many people aren't reasonable (the most famous example was X).
I now understand your usage of the word "property" was indeed legitimate.
You can build onto GPL for free without reciprocating. That's called freedom 1: the right to private modifications.