After World War II, the Japanese military was dissolved. The United States occupied post World War II Japan, resulting in the creation of the Japanese Self-Defense Forces. For most of post WWII history, the JSDF have been limited to peacekeeping operations, in the fear that another conflict will occur. 60 years after WWII, it is time for Japan to move on from occupationist thinking and allow its military to run properly.
It's been a long time since Japan didn't have a military that was completely crippled, and it really doesn't need one now. The world would not stand by while somebody assaulted Japan, so they're not vulnerable simply because they themselves cannot fire back the shots. I understand their frustrations but lets save the headaches.