It all boils down to what the breathaliser test shows. If one is over the limit, even by a bit, then one's reactions are slower and one's judgment impaired. This could cause death or maiming. Even in rural areas there are other motorists out on the roads. I'm sure you wouldn't want to be badly hurt or killed by someone whose driving was affected? That's why the law exists. Either one decides to obey The Law in its entirety (perhaps not agreeing with it all) or one doesn't and gets nicked! It isn't moral to pick and choose, that's anarchy.