There is no "I" in team, it is said, neither is there one in "blame". Upon inspection, however, more than one can be found in "responsibility".
Whenever a tragedy occurs, many people seek an explaination they can accept; some sort of reason to mitigate the unease caused by the realization that death and devastation surround the lives of supposed order that we want to believe we have created. Sometimes the most egregious incidents involve human activity; whereas the forces of nature are seen as often indiscriminate destroyers of life and limb, it is the devastation caused by the hands of people that are perceived as deliberate, and thus all the more horrific.
Therefore, the need to find an explanation for a brutal mass murder spree becomes even more urgent than for a hurricane or flood. We seek to somehow reassure ourselves human carnage comes from an easily identifiable and separate evil, a sickening but distant malevolence of which we have no part. Madness, a lack of faith, a lust for weaponry; when any single cause can be blamed for such a rampage, we allow ourselves release from responsibility and avoid the need to change our behavior. Deep down we may suspect that it takes any number of elements to combine into tragedy and horror; but complexity and multiple interacting factors make analysis difficult, and potentially fraught with hazards: such as the realization that one is passively complicit in the crime.
If our own needs becomes paramount, irrespective of all others, we run the risk of rending the fabric of community that binds our lives together. We seek power for our own protection, and risk compromising the security of others; we design to promote our faith, and endanger the spirituality of our fellows; we rigidly define our sanity, and engender the alienation of those around us; our selfish preoccupations rob us of what we seek.
Any time we commit acts of immorality for our own benefit, we run the risk of spreading ruin about us; our inability to empathize with others leads us to a lack of humanity. When we treat our fellows like creatures, should it be any surprise if they fulfill our expectations by acting inhumanely?
Without the stabilizing influence of love and acceptance, what is there to prevent any person from destructive deeds except fear?
Finally, there may come a time when pain and despair override constraints of conscience and caution; the power of control becomes paramount. The need for mastery, however brief and horrific, overwhelms all other considerations and leads to depravity and carnage. The lack of love creates a lust for power that denies humanity, and shreds society. Uncaring selfishness leads us to a ditch where the light of insight is too dim to comprehend the tragedy we have helped to spawn; and we are left stupefied by our own blindness.