Water under the bridge or not, they don't want people doing it again or supporting Russia. It could be as much as a message to the next potential Assange - don't even try. If you believe he's an enemy of your interests and working with your enemy to hurt you, I have a hard time seeing a calculation they would make that says leave him alone since what's done is done. They are going to make his life miserable forever and hope it's a deterrent. That's the realpolitik of the situation - morals ignored.