Because "beyond a reasonable doubt" is a much higher level of certainty than we have for making many decisions in life? The NSA isn't jailing people based on a

Because "beyond a reasonable doubt" is a much higher level of certainty than we have for making many decisions in life? The NSA isn't jailing people based on a lie-detector, they are just using it as a necessary but not sufficient criteria for granting security access. It's OK to deny such access based on weak or circumstantial evidence.