One should be very careful when coming to conclusions based on the Standford Prison Experiment, as there is much evidence that the experiment was very much tainted by some serious flaws.
http://skeptoid.com/episodes/4102
I didn't know any of that, thanks!
I don't think that the faults in SPE makes a house of cards out of what I was saying, however. I think it muddies the water and makes drawing any strong conclusions difficult.
That said, wouldn't you agree that some mental preparation is necessary in order to prepare for acts of violence? I would say that the guy who does his duty and stands by his convictions has probably done his fair share of mental preparation.