The immediate effect of Japan's considering going nuclear would be to concentrate China's mind on denuclearizing North Korea. China calculates that North Korea is a convenient buffer between it and a dynamic, capitalist South Korea bolstered by American troops. China is quite content with a client regime that is a thorn in our side, keeping us tied down while it pursues its ambitions in the rest of Asia. Pyongyang's nukes, after all, are pointed not west but east.
Japan's threatening to go nuclear would alter that calculation. It might even persuade China to squeeze Kim Jong Il as a way to prevent Japan from going nuclear. The Japan card remains the only one that carries even the remote possibility of reversing North Korea's nuclear program.
More than anything, Japan going nuclear would concentrate China's mind on the fact that it has another nuclear power (besides Russia) within ready striking distance. It is quite simply unbelievable that China will squeeze North Korea to abandon it's nuclear weapons program in an effort to prevent Japan from getting nukes. China will react most aggressively to the possibility of yet another an unfriendly nuclear power neaby, Japan being only a few hundred miles away. Krauthammer's logic is exactly backwards. A nuclear armed Japan will give China even more reason to want a nuclear North Korea; best for an enemy with nukes to have to contend with your nukes and your allies' nukes than your nukes alone.
Secondly, it is extremely unlikely that the other countires that occupy that region of Asia will desire to see Japan with nukes. Just as China has no desire to see another nuclear power nearby, neither does Russia. Lest we not forget, South Korea and Japan are not exactly allies. They are more like two people who share a common friend, but have a bad history between themselves. They have reason to get along-that reason being their respective alliances with us-South Kroea would have no interest in a nuclear armed Japan, let alone one whose nukes we sanctioned. And lastly, let's not forget North Korea in this equation. It is after all most likely that North Korea has acquired nuclear weapons for two reasons: to defend itself, and as a bargaining chip in negotiations with us primarily, but also with China, Japan, South Korea, et al. A nuclear-armed Japan does not further North Korea's security interests. In fact, it encourages North Korea to act recklessly to prevent or disrupt Japan from obtaining nuclear weapons in the first place.
Krauthammer also can't resist taking a shot at South Korea:
Why are we so intent on denying this stable, reliable, democratic ally the means to help us shoulder the burden in a world where so many other allies -- the inveterately appeasing South Koreans most notoriously -- insist on the free ride?
This is simply insulting. The South Koreans have for quite some time embraced an approach not of "appeasement" as he dismissively refers to it, but of communication and recognition of North Korea's interests and concerns. They are no longer so eager to confront North Korea as they once were, rightly conclucing the North Korea is no longer the danger it once was (except for the nuclear issue) and that the threat of a North Korean collapse precipitated by hostile action on our part is as grave a threat to the stability of their country as outright war is. It is not "appeasement" to abandon foolish confrontation when a strategy of engagement may work better. And let's not forget that South Koreans and North Koreans each have long-lost families on each side, which is as surely an incentive avoid war as any. South Korea is most assuredly not getting a "free ride" from us.
It's quite clear that Krauthammer subscribes to a nuclear deterrence theory a la the Cold War. But the Cold War was unique, historically speaking. A group of regional powers, each armed with nuclear weapons, do not have the same incentives to not use their weapons as either we or the Soviets did. Given that one of those powers is a tyrannical, corrupt and backwards North Korea, it is especially important that nuclear weapons be removed form the equation. Anything else is sheer foolhardines. It is impossible to believe that Krauthammer does not know this, and yet when he clearly writes everything in the context of the longed-for war in Iran, there is simply no need to be consistent or coherant.