I don't really want or expect all the nitty gritty details but there very much should have been some sort of public discussion before the Government decided they'd just scoop up all the metadatas and sort through it later. Not even allowing some public discussion about this is, to me, their biggest fuck up. It would have been nice to have at least been allowed to stand up and say, "No thanks, I don't really want my country going down this road" instead of being blindsided with it years after they started.
I also don't really buy into the "exceptionally grave damage to national security" line. I doubt this revelation has really effected the NSA's ability to continue Prism. The only damage that's been done is to our public image. The only real damage argument could be one of diplomatic damage.