A psychologist would undoubtedly agree that there is an aspect of group think that takes over in such situations (and, having experienced it, I know that it does and that it is difficult to maintain individual perspective) but the vast majority of officers are able to maintain an appropriate attitude and act perfectly properly. In fact, just like there are examples of soldiers being reluctant to kill the enemy on an individual level, even when participating in an attack on a particular objective, I have observed officers reluctant to use significant force during a public order operation even when it is perfectly justifiable on an individual level (on one occasion resulting in a person lawfully arrested for a serious offence being freed and one of the arresting officers significantly injured).