I haven't read other Replies, so I am I probably repeating someone, but it could just as well be argued that people being loud is a passive-aggressive way of asserting some kind of power. Personally, I think feeling powerless in a nation (the U.S.) in which power is the social currency has made people in general desperate to be able to assert some kind of power whenever they get the chance, no matter how trivial. Mostly that ends up being disrespectful in some way towards other people in what is really simply rude behavior.