Considering what they did in the Pacific in the past and how many American lives were lost trying to defend and stop it, should we?
There were 2,403 Americans killed in Pearl Harbor by Japan's attack. Afterward, America lost another 325,000-350,000 island-hopping to put out the fire of Japan (you could add in another million if we didn't use the atomic bomb). The direct effect of Japan, like on Korea, and its ripple effects of the war on other nations resulted in 12 to 16 million civilian losses.
Sure, we can let bygons be bygons, but blood stained every island and almost every nation in the East Pacific because of Imperial Japan. Because of that, I think it's safe to say we should only let Japan be a defensive nation, but only extend it to go beyond if directly attacked, and on the side or with the support of America.
America has a strong presence there. Enough to make up for it.
However, both Japan and South Korea should start paying more of their fair share for protection and weaponry.