hahahah..! Great point!
It’s a combination of things:
1. Concern regarding the credibility of new US security guarantees
2. Traditional craziness of the stated policies of Hatoyama’s party
3. Growing ability of the PRC to shape the US’ future (debt)
4. Accommodation of some xenophobic forces inside Japan from both the left (all war is wrong) and right (non-Japanese soldiers should not be in Japan.
I think the biggest cause is #1, followed by #4 or perhaps #2.
You’re right —it’s nuts that with the Norks up there lighting stuff off that J could be even contemplating crazy stuff like this. But they are...just wow...
I suspect their new government consists of the usual brand of leftist idiots who think that if you only distance yourself from the “imperialist” US and put on a happy smiley face, aggressors around the planet will suddenly start liking you and cancel all their evil activities. Their next step might be to unilaterally dissolve the Japanese army. Surely that will impress the Norks and show them who is the greatest peace-lover in the world!