To be fair ... it's incredibly difficult for people to make "random" selections. Even ideally, people have subconscious biases that can lead to terribly non-random choices.

Relying on a machine to make random choices gives greater assurances that the choices will actually be random. It also lessens accusations of bias (see the recent thread on Donna D'Errico's "random" selection for enhanced screening).

I've got a number of disagreements with TSA ... but this ain't one of them.