We have two seperate issues here.
First snowden thinks people should retain all copyright to the stuff they submitted. This is an option that is indeed used by a number of websites like gamefaqs, these soldatforums or everything2.com. We've chosen not to use this option because it causes a number of conflicts with the workings of the wiki. First of all articles are edited a lot, usually there are many small changes. Now, who would retain copyright on the resulting text? Each one is a derivative work of the previous ones, so you will create just a mountain of copyright layers of which it is totally unsure who owns what part of the text. And, what would happen if someone would try to pull his copyrighted works out of the this pile of copyright? It would collapse because it would make all derivative works impossible.
What if there would be problems and the community would be split? Half the articles would go to one site, the other half would go to another site. To give this wiki a good chance to survive it's essential the info remains one bundle.
This point is also very well covered by Sebastians posts.
On the other hand elephanthunter is suggesting noone should retain copyright over the wiki, meaning it is out of controll, meaning everyone can copy it, start a clone, extend the info to his or her own site. We all know the soldat community. There would be so many competing sites all trying to do the same thing. It would be a complete mess, the info would all be out of sync and noone would know where to look for the right one anymore. If you look at wikipedia there are already thousand of wikipedia clones with the same text as wikipedia (but outdated) and full of banners just to draw some google hits.
What we are aiming for with this license is to guard the integrity of the wiki while at the same time making sure noone will make profit from it, abuse it, or destroy it. Not even the copyright holders. The license restricts the power of the copyrightholder over the content it owns.
It's the middle way between snowdens vision and elephanthunters vision.
I think you are also quite wrong as far as the judicial validity of this document goes. The licenses you named have already proven it is possible to give up the copyright over content you submitted. In this case while doing this one enters an agreement with the site-owners, giving them the copyright only with certain restrictions. These restrictions fall under the freedom of contract one enjoys in Dutch law. This means the contract is legally valid so if the provisions in the contract are broken by one of the parties the contract can be enforced in court. The model the contract uses follows the way dutch administrative law works. et voilá.
The reason the license does not cover people giving up their copyright is because it is not the aim of the license to do so. The aim of the license is to restrict the copyright owners in using their copyright in an unwanted way (for example, to make money).
