I recall something from the days when I studied sociology:
...Durkheim argued that societies characterized by organic solidarity generated social solidarity not through sameness, but through interdependence. However, Durkheim also stated that this solidarity is precarious and can be abnormal, producing anomie as a consequence. Although Durkheim does not give a clear definition of anomie, it can loosely be defined as a feeling of disconnection from the moral norms and rules of a society. Under a state of anomie, there is not enough moral regulation in a society to counteract the individualism associated with a complex division of labor. In other words, a society that celebrates individualism runs the risk of forgetting to tell individuals what they can and cannot do. We can also think of it as a state of normlessness.I would argue that in some of these cases the perpetrators of the criminal acts have found their way in "groups" - often solely on-line - that provide them with a different set of norms than those of the mainstream society.
Just as members of criminal gangs have their own ethos, so do these otherwise isolated (estranged?) individuals come to seek acceptance for their eccentricities in chat rooms full of other people suffering from the same exclusion from the main society as they do, who seemingly provide a new set of norms and acceptance that encourage such that some individuals decide that to act out against the society that has caused them to feel so adrift is perfectly okay. In terms of Transactional Analysis, these individuals feel they have no worth and that society also has no worth and they may seek revenge:
I'm not OK - You're not OKI think that a person in such a state may seek to go out in a literal blaze of glory - by becoming, for instance, a major mass murderer as a way of saying, "I lived." I argue the issuance of "manifestos" by such people is a means of trying to reach into the future. The fact that such writings are often confused garbage simply reflects to confusion of the minds of their authors as they try to claim that their lives had some meaning.
This is a relatively rare position, but perhaps occurs where people unsuccessfully try to project their bad objects onto others. As a result, they remain feeling bad whilst also perceive others as bad.
This position could also be a result of relationships with dominant others where the other people are viewed with a sense of betrayal and retribution. This may later get generalized from the bullies to all others people.
This disconnection from the mainstream society, especially in this time of internet isolation, needs to be identified and addressed as a mental health issue.