I don't necessarily agree with Baez's explanation --rationalization, really--, but I agree that Casey shouldn't take a polygraph. It's hunk of junk voodoo science. It doesn't mean a thing. The results aren't even admissible in a Court of Law.
And Nancy is dead wrong about LE ruling things out if Casey were to pass a polygraph. Nancy's full of nonsense. LE wouldn't rule anything out. If Casey passed her polygraph, LE would simply deduce that the machine was wrong, or that Casey faked her exam, beat the machine. Which would be the correct thing to believe, because those machines are unreliable hocus pocus, and are beatable.
Does anyone here really believe that Casey would be released and all charges dropped if she were to pass a polygraph?
It's an absolute disgrace for Nancy Grace, a former prosecutor herself to imply that Casey would get better treatment if she passed a polygraph.