You are likely correct that the sinking of the Cheonan will not in and of itself lead to war. But when I think of rattling sabres I think of bombastic rhetoric and some military exercises - not acts of war. A non-response by the US/ROK is only going to encourage nastier provacations by the NORKs
Actually, I think the NORKs are being logical and measured. In an insane and psychopathic kind of way.
Unfortunately, you can’t reason with the insane. And a measured public display of force on our part isn’t going to help. It would have to be something along the lines of Scipio Aemilianus in Carthage.