[diesel00]

No one on the planet fears Japan arming themselves with nuclear weapons more than China.

This is mostly speculation. Sure, China doesn't want Japan to have nukes, but in the end it doesn't matter whether Japan has them or not. Japan has 1/40 the landmass of China, and 1/10 of its population. Japan could not win a nuclear war with China on its own. If Japan wants nukes only as a deterrent, then the US nuclear umbrella is good enough. It's mostly ego and posturing for Japan to have nukes. The strategic benefit is pretty minimal.

[DB]

Tell that to the Chinese of the late 1930's...

A million or more dead at the hands of the Japanese.

In addition Japan has a modern navy. Japan would be able to retaliate to the point of total destruction regardless of land mass size or damage done to their home.

[GregoryFul]

You presume that the US will live up to its committment - lots of examples in the past demonstrate that she hasn't.