In the first text, Zimbardo argues that people are neither "good" or "bad." Zimbardo's main claim is that the line between good and evil is movable, and that anyone can cross over under the right circumstances. He tells us that:
"That line between good and evil is permeable. Any of us can move across it....I argue that we all have the capacity for love and evil--to be Mother Theresa, to be Hitler or Saddam Hussein. It's the situation that brings that out."
Zimbardo argues that people can move across this line due to phenomena such as deindividualization, anonymity of place, dehumanization, role-playing and social modeling, moral disengagement and group conformity.
On the other hand, Nietzsche in "Morality as Anti-Nature" also argues that all men are capable of good and evil, and that evil is therefore a "natural" part of people. However, his opinion is different from Zimbardo in the sense that Nietzsche believes that judging people as "good" and "bad" is pointless because morality is anti-natural, and we have no good reason to believe that our behaviour should be modified to fit these precepts.
I think that number 3 is the answer you're looking for.
