And that is written... where exactly? You're not allowed to move CHECKED bags from the cargo compartment to the passenger compartment but you MAY move already screened carry on bags (which have a special ALREADY SCREENED neon green tag in united) from the cargo compartment to the passenger compartment.

Not only would I say this in public, I would do it in front of a safety inspector grinning the entire time. Besides, most of the time they're not even in the cargo compartment yet -- they're on the rack.