There are substantial cultural differences in those countries. Even if tomorrow you would allow any weapon in Japan it won't change anything. There will be no school shootings (at substantial amount). Japanese people conditioned differently.
Can you guarantee me that the culture will hold back gun violence?
Presence or absence of weapons doesn't affect if someone will use it or not. Getting or making a weapon is relatively easy task even in Japan.
Growing a cohesive society where people use other means to cooperate instead of assaulting everyone who disagrees with their opinion is most important
Yeah No. When weapons are absent, the probability of using a weapon is exactly 0.
When weapons are cheaply and easily available, the probability is definitely not 0.
Those who wish to create mayhem, can and will, get weapons one way or another. Happens all over the world. No amount of laws or severity of punishments can change that.
But, gun restrictions prevent impulsive actions, and actions or situations exacerbated by the false security that having a gun gives, or plain right idiots who don't know how to safely handle guns.
How many mass shootings happen in Japan? How many kids are killed in Japanese schools because someone barged in with a military grade assault weapon, tactical gear and unlimited ammo? How many gun killings per capita happen in Japan? How many people per capita in Japan have gun violence as a priority as compared to the US?
So many questions that have answers in favor of gun control are ignored.
Guns are in-compatible with human nature (The off chance of a bad decision for revenge or murderous rampage is high enough to ban guns). Because they distort the power in favor of the gun bearer.