Name your very best example that will prove me wrong. It should be so simple. One example, that's all it takes. Take your time, make sure you've got a good one. I'll tell you that not once, not a single time in over 17 years, have I ever seen a single example of this argument hold up under scrutiny.
Oh wait, you already did:
> Because naked men are a shared concept Michelangelo's David is not protect-worthy?
Ah yes, Michelangelo's David. A work free of copyright built under commission! Thank you for again pointing out the futility of the defense of copyright.