You are correct. Everyone should have to go through the metal detectors, including congressmen/women. How easy it would be for someone to counterfeit a pin and get waved on, bypassing security.
Well, since McKinney admits to not wearing her pin, we really don't know who is in possession of it, do we? No need to counterfeit. Was she the one who gave Sheehan a ticket to the SOTU address?