I think in order to have a discussion about this you would need to define what you think is politeness. Even politeness can be relative to the society you are in. Example: Here if you pick your nose while talking to someone that is considered rude, however in other cultures doing that shows that you care about your hygiene. So what you may view as rude may be the normal conduct of the people of that area. As for the quote I feel it means that if people are armed they are more likely to behave in such a way as to try not to escalate situations into a fire fight because neither party wants to loose their life. It would be a similar idea to the so called M.A.D. (Mutually Assured Destruction) policy. If Russia was to nuke us we would nuke them and visa versa, neither side wanted to die which helped keep the cold war from turning hot. That is my take on it.