I am afraid what you argue about Japanese nuclear aspirations is partly true. There is thinking emerging within Japanese strategic community, that US extended deterrence is a bogey and unlikely to work. US will not risk nuclear contest with China or NK for protecting Japan.

A more constructive argument of Japan forsaking NW is that as a non nuclear weapon state both China and NK would think twice in attacking Japan and face global operribixm. In case situation in East Asia continues to deteriorate, Japan could rethink its nuclear option!!!