7 social processes that great the slippery slope of evil:
1. Mindlessly taking the first small step.
2. Dehumanisation of others.
3. De-individualisation of self (anonymity / being part of a crowd).
4. Diffusion of personal responsibility.
5. Blind obedience to authority.
6. Uncritical conformity to group norms.
7. Passive tolerance of evil through inaction, or indifference.
From Ted: http://www.ted.com/index.php/talks/philip_zimbardo_on_the_psychology_of_evil.html