"Emergence of good conduct, scaling and Zipf laws in human behavioral sequences in an online world" http://arxiv.org/abs/1107.0392
"...In their virtual life players use eight basic actions which allow them to interact with each other. These actions are communication, trade, establishing or breaking friendships and enmities, attack, and punishment. We measure the probabilities for these actions conditional on previous taken and received actions and find a dramatic increase of negative behavior immediately after receiving negative actions. Similarly, positive behavior is intensified by receiving positive actions. We observe a tendency towards anti-persistence in communication sequences. Classifying actions as positive (good) and negative (bad) allows us to define binary 'world lines' of lives of individuals. Positive and negative actions are persistent and occur in clusters, indicated by large scaling exponents alpha~0.87 of the mean square displacement of the world lines. For all eight action types we find strong signs for high levels of repetitiveness, *especially for negative actions*..." [emphasis added]
popularization: "Virtual World Study Reveals the Origin of Good and Bad Behavior Patterns" http://www.technologyreview.com/blog/arxiv/26967/
"...Thurner and co found that positive behaviour intensifies after an individual receives a positive action.
However, they also found a far more dramatic increase in negative behaviour immediately after an individual receives a negative action. "The probability of acting out negative actions is about 10 times higher if a person received a negative action at the previous timestep than if she received a positive action," they say.
Negative action is also more likely to be repeated than merely reciprocated, which is why it spreads more effectively.
So negative actions seem to be more infectious than positive ones.
However, players with a high fraction of negative actions tend to have shorter lives. Thurner and co speculate that there may be two reasons for this: "First because they are hunted down by others and give up playing, second because they are unable to maintain a social life and quit the game because of loneliness or frustration."
So the bottom line is that the society tends towards positive behaviour."
Well, maybe in the game they studied, _Pardus_. I couldn't say about Wikipedia...