Linus Torvalds explains why he is inclined to stick with version 2 of the GPL rather than adopt the draft of version 3 that has been proposed:

My initial reason for my original license (which was also "you must make changes available under the same license") was not crusading, but simple reciprocity. I give out source code - you can use it if you reciprocate.

In other words, to me, the GPL "give back source" is an issue of fairness. I don't ask for anything more than I give. I ask for source code and the ability to incorporate your changes back into _my_ use, but I don't want to limit _your_ use in any way.

So in my worldview - not as a crusader - the GPLv2 is _fair_. It asks others to give back exactly what I myself offer: the source code to play with. I don't ask for control over their other projects (be they hardware or software), and I don't ask for control over copyrights (in the kernel, people are _encouraged_ to keep their copyrights, rather than signing them over to me).

I only ask for exact reciprocity of what I give: the license for me to freely use the changes to source code that I initiated.

The GPLv3 fundamentally changes that balance, in my opinion. It asks for more than it gives. It no longer asks for just source back, it asks for _control_ over whatever system you used the source in.

This is a good assessment -- v3 is not a license within an existing system of intellectual property but an attempt to create a new system. In weird way, it is like legislation, and it comes complete with legislative history in the form of explanations, FAQs, and other devices associated with laws rather than contracts.