Please explain. Did the previous terms also require anything that debatably required getting permissions from copyright holders beyond those granted by, e.g. GPLv3?
The new terms do not grant permission to Github to do anything that they weren't already doing. If you take the view that this agreement is not compatible with a particular software license, then publishing the same software on Github prior to the changes logically must have been a license violation.
What? No. Prior it meant Github was violating your license. Just because they were already doing it doesn't mean they had a right to do so. Now, it means you're granting them a license. I'm not a lawyer, and I have absolutely no clue if it's even legal for Github to change their ToS like this. But I assume if you don't have the right to grant this attribution exception to Github (because you don't own all the code) and you don't remove your code from Github, then you are now also in violation of the rights of contributors to the project that didn't consent to this waiver.
