You're right; failing to detect weapons (and thus letting people die) is a fatal error that can't be corrected. Failing to correctly id you is something that can be corrected by a human afterwards. I'm much happier to let a system incorrectly id someone than to let them onto a plane with a weapon.

That said, this seems like just one of many potential id methods that would comprise a larger system (facial recognition, fingerprinting, etc).