Flawed, ostensibly objective tests for subjective, volatile, potentially unkowable information (ie polygraphs, job interviews, school aptitude tests, IQ tests, etc) adre all about passing the buck to the next guy. If it ever turns out that someone is an enemy spy, then the person who hired him can't be blamed, because he "passed the polygraph". It's about plausible deniabiltlity and CYA.