Every man in Switzerland has a gun for national defense, yet the murder rate is very low. Why?

Because you're lying.

I already replied to that claim a couple of hours ago when you posted it in another thread.

Switzerland's murder rate is substantially higher than that of Austria, the country to which it is most similar in every other respect except gun ownership.

It also has a very high incidence of suicide by gun (though despite frequent claims to the contrary, its overall suicide rate is not all that high, less than double the UK rate and not much higher than the US).