During the years of Western expansion most everyone was armed.  Armed robbery by the highway men was far more common then than it is today.  Your theory has never been actually proven to be more than a talking point without definitive proof.  
Thieves and robbers have been with us since the time before the bible was written.  The problem exist around the world in varying degrees.  In countries with severe punishment there are those who risk having a limb cut off as they rob and steal.