Meet the new boss, same as the old boss: you dispose of any capitalist crooks, social relations in a capitalist system will happily replace them with others who fulfill the same criminal functions. We can't solve the problem by lining a few bad apples up against the wall, however cathartic that may be.
[WS:] What makes you think that the problem is solvable by any other means?
Oftentimes, "systemic" explanation are a modern, rationalist versions of the good old sorcery - attempts to "domesticate" unsolvable problems, buying peace of mind by making people believe that solving a particular problem(s) they face is within human reach, if the right ritual is exercised. In the good old days, shamans would cast their spells, make the sacrifices, and perform magic rituals before their fellow tribesmen would engage in risky and unpredictable activities (cf. Bronislaw Malinowski's anthropological work on Trobriand Islands).
Modern societies, where rationality is the king, replaced these irrational divinations with rational ones, such as risk management (cf. Lee Clarke, _Mission improbable: using fantasy documents to tame disaster_ http://leeclarke.com/ ), market forecasting and seemingly rationalistic techniques of controlling undesirable aspects of human behavior. The right wing version of these rationalist divination techniques is the "discipline and punish" approach (c.f. Michel Foucault book under this title). The left wing version of these divination techniques is the "change the system" approach - a belief that an "ideal" social system can be created to eradicate all human vice and depravity.
People believe in these mythologies, which they adopt based on the political leanings, when they face human behavior that they find deeply troubling. They would find it even more troubling if they realized that the behavior is not preventable and out human control. An example of it is random school shooting that can happen anywhere, even in low crime low violence societies such as Finland http://news.bbc.co.uk/2/hi/europe/7082795.stm. One way of rationalizing such behavior is to invent purported causes of it that are within the reach of possible societal actions - such as gun control (left wing), severe punishment (right wing), more education (left wing), beefing up security (right wing), radical social transformation (left wing), getting rid of undesirables (right wing) and so on.
These fantasies are rationalist, because they can muster some empirical evidence that the purported causes are related to the undesirable behavior in question under some circumstances. However, they are fantasies nonetheless, because they make a much stronger causal claim than the evidence permits. By so doing they transform the purported "cause" from being one of many contributing factors to the ultimate cause or _the_ sufficient and necessary condition of the behavior in question.
Stated differently, any of the purported causes listed above - gun control, severe punishment, more education, beefing up security, transforming social relations or incapacitating "undesirable" elements (gangsters, career criminals, corrupt leaders, etc.) - is likely to have some effect on the behavior in question (school shooting, or violent crime in general) under some circumstances. However, none of them - individually or combined - is/are likely to eliminate the behavior in question altogether. The latter belief is merely a rationalist myth that helps people coping with troubling, unpredictable and thus uncontrollable aspects of human behavior and life in general.
Wojtek