"What's stopping me from licensing everything under AGPL?"
Absolutely nothing. In fact I'd love to see more things licensed in that way.
There is some stuff at http://gplv3.fsf.org/ especially if you go to the
Comments tab which lets you review various Discussion Drafts and see what
parts of the license people were commenting on based on color codes the more
comments the darker it gets. They also provide some of their Rationale
documents too. http://gplv3.fsf.org/gpl3-dd3-rationale.pdf has the rationale
for Discussion Draft 3. But it's probably good to look over all those
Rationale documents. There's one to go with each of the Discussion Drafts.
There were 4 Discussion Drafts made.
Also, the FSFE has collected some information and even videos:
https://fsfe.org/campaigns/gplv3/
