This guy makes a number of assumptions not the least of which is that the Japanese have simply abandoned centuries of tradition and belief and can now be completely trusted to exercise military power responsibly. I have no idea how they will exercise military power. I believe they have the technology to rival our own military if they wish and that they can become a nuclear power very quickly. I also believe that once they have this power we can only hope they will exercise it prudently and as an ally because once they have it we challenge it at our peril. The last 60 years may be enough to uproot all those ancient beliefs and traditions. But the Japan is not the U.S. and they have their own ideas and ideals and may discover they also have old ambitions that need only the hope of fulfillment to reawaken.
No, the piece makes no judgments on Japan's "trustworthiness" past that which might be expected of any nation. The point is that Japan is no longer acting the child under the USA's wings and will take to their own defense if they continue down this path.
Further, you seem to be assuming they WON'T be trustworthy. Why is your assumption any better than the writer's?