The bystander effect can explain the persistence of certain types or instances of rights violations. If many people witness a person in distress, then it’s the less likely that any one person will help. “I could help, but I’m sure someone will”. Numerous experiments have proven the effect. Virtually all of them find that the presence of others inhibits helping, often by a large margin. The probability of help is indeed inversely related to the number of bystanders, although not necessarily one-on-one. More precisely, the effect occurs when bystanders are strangers; when bystanders are friends help is usually forthcoming.
What are the reasons for this effect? Hard to tell, but social influence may be one: bystanders monitor the reactions of other people in an emergency situation to see if others think that it is necessary to intervene. If everyone first looks at the others, then you have a vicious circle of influence. Since everyone is doing exactly the same thing – i.e. nothing – they all conclude from the inaction of others that help is not needed. Diffusion of responsibility may be another reason: when a lot of people are present, they all assume that others carry more responsibility to intervene, because others may be seen as closer or stronger or first on the spot (this is also the thinking behind the firing squad or the Japanese procedure for capital punishment). The fear of being harmed or of offering unwanted assistance may also explain the effect.
Increasing urbanization and improved knowledge of everyday events (by way of better information systems such as the internet) can make the bystander effect more common, and can therefore make it more difficult to stop rights violations.
There’s a peculiar reaction to the bystander effect described here. And here are some notorious cases of the effect. More on the possible causes of rights violations here.
Can bystanders who cheer on a criminal invoke their right to free speech, or can the government prosecute them and hence limit their right to free speech? An infamous example is public rape, a particularly horrendous crime in which a man or group of men rapes a woman in a public space, for example a bar, while being loudly encouraged by a group of bystanders, most of whom will probably be sexually aroused by the spectacle. The movie “The Accused” offers a classic depiction of such a crime, and is based on a real-life public gang-rape.
The case of cheering bystanders and their right to free speech is similar, although not identical to some other cases that I discussed previously, such as hate speech, speech that teaches the methods of illegal activity, death threats, and incitement to violence. These cases are similar because it’s assumed that all these forms of speech can produce violence or can make violence more likely.
Eugene Volokh, normally very hesitant to allow restrictions on free speech, says that prosecution should be possible
on the grounds that the cheering tends to encourage the criminal and thus constitutes “abett[ing].” “An aider and abettor is one who acts with both knowledge of the perpetrator’s criminal purpose and the intent of encouraging or facilitating commission of the offense.” People v. Avila, 38 Cal. 4th 491, 564 (2006). (source)
In some circumstances, the bystanders are even strict accomplices in the sense that they aid the criminal in his or her actions: their cheering may make it impossible for others to intervene because they seal off the crime scene, or the cheering can include precise instructions. One can also imagine cases in which the criminals wouldn’t have acted if not for the cheering. But even if the bystanders are not strict accomplices in any of these senses, they are surely guilty of criminal failure to assist persons in need. Instead of cheering, they should have called the police. So, in all these cases, the bystanders help the crime occur, even if all they do is vaguely encourage someone. Hence they cannot claim that their right to free speech should protect them against criminal prosecution.