It was all so innocent, that's why I lied about it

Kevin Drum asks the right question about Libby:

Take Bill Clinton. He lied too when he denied having an affair with Monica Lewinsky, but in his case everyone knew exactly why he had lied: because he didn't want anyone to know he was getting blowjobs in the Oval Office. And most of us took that into account. First, because it plainly had nothing to do with the official exercise of executive power, and second, because pretty much everyone figured they might very well have done exactly the same thing in his position. It was understandable human weakness. So while we might not have approved, most of the public decided it wasn't a hanging offense.

But Libby is a different case entirely. The conservative community wants us to believe that Valerie Plame wasn't really undercover at all. They also want us to believe that outing her was, in fact, part of an entirely legitimate effort to explain that Dick Cheney hadn't been responsible for sending Joe Wilson to Niger. And finally, they want us to believe that none of this was part of a coordinated plan. Plame's name was merely mentioned in an offhand way here and there when reporters brought up questions about Wilson's trip.

But if that's the case, then why did Libby lie? Deliberately and repeatedly? Richard Armitage fessed up almost immediately. Ari Fleischer fessed up. Karl Rove had to be pushed, but eventually he fessed up too. Only Libby lied.

Why? If nobody actually did anything wrong, what was he hiding?