Although I haven't had a chance to study the article by Zimbardo, the aspect that interests me is the emphasis on how social situation determines the ethical / decision making process. He makes the claim that even those with 'high moral' feelings were still changed through extreme social situations (like in Nazi Germany) or were likely to be changed. This is something that we need to learn when we decide on how to make ethical decisions - we need to realise that we are strongly influenced by our environment and that we can be 'seduced' into doing bad things. Once we realise this we can work to minimise these effects.
It is also important that governments and organisations working for social change realise that a good social environment is crucial for a good society. I don't think you can just expect people to behave 'properly' - crime, terrorism etc needs to be fought not only in the minds but in the social conditions of where people live.