I believe after what the Japanese have done to show their allegiance to us in the past, we should have taken Okinawa as a strategic foothold in the Pacific and not given it back. With that being said, yes, they should keep a military force, however- it should be used for defensive purposes only as it is now.
With this new constitution, they are allowed to fight in defense of an ally. In the previous months, Japan has been selling submarines to Australia. Does this make them an ally? What is next for the Pacific? If Aussie is to take on China, Japan can then follow, which draws American in and sparks an all out war in the pacific once more.
People were against this as it is a pacifist country after WWII, but we made the constitution as we won the war with lots of tears, bloodshed and stars hanging on widows and mothers doors. This should not have passed, nor been introduced IMO.
In fact, let's forget all security treaties/Constitutions signed. Let's give up on Ukraine and see what Russia does, etc. because that's basically what Obama let happen yesterday.