even if drugs were legal and completely decriminalised, it doesn't make them a sensible thing to do when you have a job that directly impacts other peoples lives, safety and wellbeing, anymore than it is a sensible thing to get in your car and drive home after drinking a bottle of (legal) vodka.
also if you are a coke head that pays for sex, you are a liability to the reputation of the rest of the government, so this guy clearly has no respect for his colleagues or they are all at it, or they all believe they are above the law and beyond reproach.
as they said about the 'snoopers charter' - if you have nothing to hide you have nothing to fear. apply their own logic to their own drug testing, and i would expect a lot of protestation about how blanket testing has a chilling effect.