Good news or bad news?
Arguably, the mutually assured destruction with nuclear missiles brought some extra safety to the world: The countries with nuclear weapons could relax their military readiness because there would be enough time for later retaliation, even if only few nuclear missiles would remain operative.
Even with a country like North Korea, one might imagine that the existence of nuclear weapons raises the stakes sufficiently that a future war becomes improbable.
When the US manages to change the game with missile defenses, they might set the world back to a state where countries keep a large nuclear arsenal on a hair trigger -- just to ensure that they can launch in time to get some missiles through the defense shield.
Is that a good thing or a bad thing?