My point is saying Japan has fewer murders and then using that as a basis to estimate intelligence is fucking stupid if you ignore the fact that murder is a crime and japan has fewer crimes overall. Similarly, using Sweden as a comparison makes no sense. What Sweden and Japan have in common isn't firearm laws or intelligence, but very small immigrant populations.
Increase the size of the immigrant population of either country to 25% of the total population and crime in those countries will skyrocket. This isn't because immigrants are less intelligent (though they may be) or simply evil, but because as they attempt to merge with the greater population, traditional values will conflict with newer ones.
When the values of a society change, but the means of achieving those values either don't work of simply don't exist, people will attempt to find alternatives means of achieving the goals they believe society expects from them.
Put simply, society values self sufficiency, but you have no job, no means of getting a job, and no money. Alternative? Steal money. Goal met.