Not quite sure what you'd ban in Japan, you already can't have much of anything and haven't since WWII. However their suicide rate seems to keep climbing. They don't do it with guns typically, but rope and gravity seem to be their top two methods.
My only point is to measure the effectiveness of anything all things must be considered. To state Australia's gun related homicide rate fell after the ban sounds great, but so did ours with no ban and at nearly the exact same rate.
I'll take personal freedom and responsibility for my own safety. Apparently most Americans agree with me.
Suicide, imo, isn't an issue concerning gun bans. I think ones purposeful attempt to harm another is more legitimate. For the individual, the firearm is the most efficient way to dispatch someone... easily, quickly, and without a mess. A ban, while distasteful to us, imo probably works in a number of places. Even if the assaults stay on par with previous years, some would say that injury is preferable to loss of life.