This. The original argument is sideways. When contributing code, you claim to have written it yourself and you grant a copyright license to this work of yours.

This. The original argument is sideways. When contributing code, you claim to have written it yourself and you grant a copyright license to this work of yours. You don't claim the contributed code does not infringe on any patent. (How could you?? Normal code contributor has no idea how to check that.) So the only evil plan the CC0 prohibition foils (a patent holder contributes code needing patent license under CC0 and later sues for patent infringement) needs only to be slightly modified: the patent holder asks/hires someone to contribute such code. This person grants all rights using BSD0 but obviously cannot grant a patent license to someone else's patent, so the patent holder can still sue.