Putting video cameras and facial-recognition databases into an otherwise straightforward and simple one-way-door system... is many things, but "straightforward" is not going to be one of them. Consider: hats, scarves, small children, people looking at the floor...
moreover, if the US government wants to take pictures of your face and arrange an arrest, they can get it at airport entry (or customs) which are far more detention-like procedures, and a place you could actually enforce the measure: the guard tells you "look at the camera, please" before waving you through.
So I don't really see the "exit-turnstile-chamber plus camera" threat to be particularly worrisome. It's a poor choice of place to implement camera-system abuses.
moreover, if the US government wants to take pictures of your face and arrange an arrest, they can get it at airport entry (or customs) which are far more detention-like procedures, and a place you could actually enforce the measure: the guard tells you "look at the camera, please" before waving you through.
So I don't really see the "exit-turnstile-chamber plus camera" threat to be particularly worrisome. It's a poor choice of place to implement camera-system abuses.