As in this episode of KCRW's The Business, it's often MPAA Chair Joan Graves who appears defending the system. And the defense cited time and time again is that the MPAA ratings are decided by parents - not film experts, or psychologists, but honest-to-goodness, salt-of-the-earth, God fearing parents.
It was probably the 20th time I heard this argument that I was reminded of this nugget of wisdom, spoken by Keanu Reeves in Parenthood. It does well to summarize the wisdom, reliability and exclusivity of "parents" as a group.
"You need a license to buy a dog, or drive a car. Hell, you need a license to catch a fish. But they'll let any butt-reaming asshole be a father."