Many people think it is essentially fact that Karl Rove broke the law. Well, it's not. Not even close.
Most importantly, there's no evidence that Rove knew Plame was undercover (if indeed she was: that still is not publicly known, though it seems likely, else why investigate it?). The Cooper e-mail says only that Rove identified Wilson's wife as working for the CIA on WMD, not that she was undercover. There's simply no reason to think Rove certainly knew she was undercover.
There's also the possibility that Rove didn't even tell Cooper until he knew Novak had the information and was going to have it published. So in this possible scenario, Rove didn't know she was undercover, and told Cooper only that information which was already essentially in the public domain (that is, it certainly would be in the public domain by the time Cooper's story ran).
There is certainly a lot more to this story than any of us know. The Island of Conclusions may look good from afar, but it is less attractive once you get there.