I certainly think, in terms of psychology, that we all tend to act differently when we feel we are being supported by a group. The idea of deindividuation certainly comes to mind. When we are in a group, it has been proven that we are more likely to act out. It is more difficult to punish a large group, rather than one offender, and it is also easier to conceal your identity in a large group. It simply feels easier to act out, because everyone else around you can provide a sort of shield from consequences.
It is also important to look at groupthink in psychology, in which individuals go with the flow of the group (even if the group has silly or destructive ideas), simply to keep the harmony of the group. If an entire town is vandalizing a local cornerstone, the peer pressure to conform to that group standard will mount. It will seem easier to simply conform to the group's wants and desires, rather than stray from it. Look into the Solomon Asch conformity experiment!