[knallfrosch]

I always thought the workings of polygraphs were common knowledge.

It's fiction. Analysts get scared and don't do anything wrong preemptively. Analysts admit stuff they'd never do otherwise. The agency gets to show who's in charge. It creates a legal fiction that allows you to abuse your employees. It creates a fiction that the abusers themselves can believe in.

Why should the believe in the non-working polygraph be any weaker than in a nonexistent god?