I’ve had a long fascination with the Lucifer Principle by Phillip Zimbardo (see video). A lot of his anecdotes are from the Stanford Prison Experiment, and other like it. The crux of the argument being that humans have immense capacities for doing good and doing evil, but the side they choose is a function of their environment. One of the most poignant points are that anonymity, and therefore the loss of accountability are necessary conditions for misbehavior.
I think the web has its own share of evil. If you look at the past few years the web has been a cat and mouse game between spammers and spam fighters. Phishing is and continues to be a large problem. Comment/conversation streams all over the web are filled with hateful spewing, flaming, and trolling. If we connect it back to what Zimbardo observed in the physical world, it makes sense: the internet provides a veil of anonymity therefore resulting in bad behavior.
Now if we take a look at Facebook the landscape looks very different and the reason continues to make sense and be consistent with the aforementioned. Facebook provides transparency, and the loss of anonymity. The environment online is changing and so is the behavior. Companies are less likely to spam for the fear of being banned. Fake identities are hard to foster. Facebook has changed the rules without even knowing it, but in a good way.