I do understand why you'd say it, because it sounds balanced and reasonable at face value, but time and time again we've seen what happens when the word of the GPL is followed, but the spirit isn't.
Centralising copyright ownership in a single organisation (particularly a commercial entity which may be acquired or choose to protect its existence violently) is a threat to communities which aim to co-develop.
In a true co-developing community, a single participant doing something stupid or destructive doesn't hurt everyone else.
In a single-entity, single-owner project, only one participant needs to do something stupid or destructive and it will affect everyone else, and they may not have any say in the matter. Corporate takeovers, bankruptcies, falling profits, new leaders... all these things can provoke such a situation.
That won't happen in projects like Apache and GNOME, which are truly collaborative, decentralised, co-developed, multi-author, multi-copyright-holder projects.
So you can talk about "the spirit of GPL", but this spirit is too tainted with a political agenda that made it a double edged sword.
Heck, the biggest supporters of AGPL are companies that sell web-related platforms or libraries for a living and slapping an "open-source" label on such packages is good marketing.
Here's some food for thought: if OpenJDK would've been licensed with Apache version 2, a fork would have already happened. GPLv2 was chosen for a reason ;)
Are you fine with someone integrating your code into a GPL project that competes with you, and potentially out-competes your project?
I do think the opposing position has merit, I just don't take the same position personally.
Either the GPL is sufficient to keep participants harmonious or it isn't.
This essay embodies everything that keeps the free software movement from greatness.
Alas, the movement is perpetually suspicious of those who want it to flourish.
The statements above are also the OPs matters of opinion.
Because there's a lot of grey area between those binary states, and plenty of examples of the GPL being used for good and/or evil to various degrees.
Either the GPL is sufficient to keep participants harmonious or it isn't.
You could say I'm arguing that the GPL isn't enough to keep participants harmonious, and therefore accepting the binary nature of your claim... but in the context of your post, I think you're conflating the GPL with all kinds of other social interactions in FLOSS projects, and carving its impact into binary positions can't give you an answer based on fact and experience.
(phew)
If all the contributors own their part and license it under the GPL, this ensures a level playing field. The GPL provides a shield for all involved. If they all assign copyright to a single entity, they lose their shield and this entity has the advantage. This is why that entity should provide something in return: a GPL-like guarantee.
How can this be said with a straight face in a most unharmonious essay that decries 1) the practice of adding copyright assignment (above & beyond the terms of the GPL) to a non-FSF entity and 2) suggests that the GPL is not sufficient and that additional promises must be made by that entity.
Either the GPL is sufficient to keep participants harmonious or it isn't.
This essay embodies everything that keeps the free software movement from greatness. I'm grateful that free software was there for me during the dark ages of computing, but I wish it could be more than an escape valve from monoculture. Alas, the movement is perpetually suspicious of those who want it to flourish.
Edit: jdub, I appreciate your reply. Could you be more specific about exactly which statement of fact is incorrect? "This is factually incorrect" sounds ominous, but I don't see where you contradicted anything I wrote. Nothing about our perspectives seems mutually exclusive at all.