If you want to lose faith in humanity, I highly recommend watching Compliance. Even with knowledge of the Milgram experiment and the Stanford prison expiriment exploring how easily normal people can be coerced into compromising their morals, it is quite shocking to see how far people will go in this film based on a true story.

About 10 minutes in to the movie, I thought to myself, "Ok, this is where I'd bail out", and yet the movie goes for another 80 minutes of increasingly unbelievable behavior inflicted on a girl by her coworkers at the request of an authority figure on the other end of a phone line. At the end, I was pretty incredulous and did some brief research on the real events, believing they must've been embellished. To the contrary, every hard-to-believe event really did happen basically as presented. You can read up on it yourself if you want, but I recommend going in to the movie as cold as possible.

One of the common criticisms of the movie I see is that "all the characters are unbelievably dumb." I think the cast does as good a job as possible with the material, and the feeling of disbelief is exactly what they're going for. Recognizing how low we can sink is the first step to prevention.