Originally Posted by QueenOfCoach

Because the captain is in charge of the aircraft. If the captain believes a passenger's attire could be a safety hazard, then the passenger needs to be taken off the flight.

I dress for air travel with my own personal safety in mind. Flat, sturdy shoes. Cotton calf-length skirt and blouse. Layered for temperature regulation. Too hot? Take off a few layers. Too cold? Put more on.