People end up on the no fly list. Kids in wheelchairs and little old ladies get felt up for bombs and are put through a needless trauma.
Just, amazing. Purely security theater.
TSA: nothing for something
Consider two passages. One has a mantrap or airlock style set of doors which only permits two people per minute. The other has a set of turnstiles which -collectively- permit six-hundred people per minute.
Through which passage are you going to fit the most people in a sixty-minute period?
Consider also that -regardless of how many people you fit through the passage- at the destination of each one of those people is an orderly queue designed to never be overloaded. This means that the only thing lowering throughput at the passage does is lengthens the queue to pass through the passage. If you lengthen that queue, then folks waste more time waiting in that queue; time that could be usefully spent doing anything else.