pros and cons of Japan going nuclear

One strategic factor against Japan acquiring a nuclear arsenal is that the country's small size cancels the principle of mutual destruction, HE SAYS?. Japan's concentrated population centers would more than likely be wiped out after a first strike.

And, he adds, policymakers who champion going nuclear are also failing to consider another issue - those who have their finger on the button in Pyongyang are unlikely to hew to a rational approach.

"Nuclear deterrence will not work against an irrational or desperate opponent" and would be unlikely to prevent the desperate last acts of a North Korea on the brink of collapse, says Taoka

The point of Japan going nuclear is not defending against Korea but against China,

US security analysts appear divided on the matter. Brad Glosserman at the Center for Strategic and International Studies' Pacific Forum in Hawaii says that nuclear weapons would damage Japan's core security interests and destabilize Northeast Asia by potentially threatening the US-Japan alliance. Others say that a nuclear Japan could act as a counterbalance to North Korea's greater weapons capability

The US opinion is the most decisive.

In order to acquire nuclear weapons, Japan would have to violate or withdraw from a number of international agreements, including the Nuclear Non- Proliferation Treaty (NPT). Such a move would isolate Tokyo and ruin its chances for permanent membership in the UN Security Council, a long cherished goal.

That is the important point.

North Korea already views Japan as a vassal of the US,

Can't say it is inaccurate・・・・ the US has been generous.　Some Japanese want the US to add Japan as
51st state.

and urged over the weekend that Tokyo be left out of the six-party talks on the grounds that the Abe administration are "political imbeciles," incapable of recognizing the North as a nuclear state.

With neighbors like these, Japan perhaps has good reason to discuss a broader range of military options. The next step may be a revision of the nation's Constitution, which prohibits the use of force. Abe wants to enact a new national charter within five years that has a more realistic approach to security matters.The Christian Science Monitor

The constitution does not forbid Japan going nuclear. It allows Japan to have military force to defend itself.