The polygraph acts like the pot use question for many US law enforcement positions. People rightly recognize that it's absurd, but for the wrong reasons. It's not there to select for straight edge people who have never smoked up, but to select for people willing to bend the truth for the sake of making procedures have the expected outcomes. Law enforcement doesn't want the guy who feels compelled to cost himself a job by being honest about a roach when he was 14, not because he did something illegal, but because when asked on the stand whether he's confident evidence bag #14 never left his sight he's likely to let the truth get in the way of the legal machine.
The polygraph foremost is a way to arbitrarily filter people for reasons that interviewer would rather not reveal, and secondly to select for people willing to put up with the theatrics of procedures while being indifferent to their supposed purpose.