Statistics from places like Canada or Switzerland (which have and historically had lots of guns per capita) demonstrate that weapon availability itself does not cause such violence.
You compared Japan's rate of violence to America's, and conclude that America's policies must be the cause. This is wrong because you're comparing completely different groups of people. What you should be doing is to compare Japan's rate of violence to the rates among Japanese immigrants in America.
If you want to figure out which variable matters you need to isolate that variable. And if you do, you'll discover that results come from the people much more than the policy.
The difference between America and these places is that America harbors specific subcultures which glorify violence, gangs, drug trade, criminality and generally antisocial behaviour. If you're not involved in these subcultures, or in close proximity to them, you really have nothing to worry about. Hyper-rare stray bullet incidents "in a decent part of town" don't change this. (I recognize that some people can't escape these subcultures and suffer from them, but again, this is a subcultural problem).
You compared Japan's rate of violence to America's, and conclude that America's policies must be the cause. This is wrong because you're comparing completely different groups of people. What you should be doing is to compare Japan's rate of violence to the rates among Japanese immigrants in America.
If you want to figure out which variable matters you need to isolate that variable. And if you do, you'll discover that results come from the people much more than the policy.
The difference between America and these places is that America harbors specific subcultures which glorify violence, gangs, drug trade, criminality and generally antisocial behaviour. If you're not involved in these subcultures, or in close proximity to them, you really have nothing to worry about. Hyper-rare stray bullet incidents "in a decent part of town" don't change this. (I recognize that some people can't escape these subcultures and suffer from them, but again, this is a subcultural problem).