There is a series of psychological thought experiments (the Trolley problem) in which participants are asked moral questions which produce increasing levels of discomfort. These experiments - investigations of philosophical consequentialism - are a litmus test to the commitment of a utilitarian's position but this post is not really about that issue so much as about how it is connected to our feelings about personal and impersonal violence.
Two of the trolley problem scenarios concern what you should do if you see a trolley on some rail tracks hurtling towards a group of 5 people who will die on impact. In one scenario you have a lever that will divert the trolley onto another track but, on the other track, there is a single person who will then be killed by the trolley. Should you pull the lever? In another scenario you are standing on a bridge alongside a fat man and you know that, by toppling him over the bridge, he will halt the trolley but die in the process. Should you push the man?
Even if we cannot come to a conclusion about what actions are right for these scenarios most of us will feel that the second scenario presents a more challenging moral conundrum, and its resolution has been debated at least since the time of Thomas Aquinas. But philosophy and morality aside the scenarios point to an aspect of our innate makeups that we need to acknowledge if we are to make sense of why individuals and societies act as they do under stress. We might call this aspect of us our human empathy.
I offer the speculation that whatever it is in our psychology which makes us more leery of positive action in the second scenario is also what has contributed to the greater slaughter of people (military and civilians) in modern warfare.
Of course the huge mortality rates in modern warfare are definitely connected to another factor: the much greater killing power of weapons of mass destruction (WMD). (By the way, the definition that WMD just means nuclear weapons is, I think, completely arbitrary. The London Blitz: 40000 dead , the Dresden firebombing: 25000 dead, the Hiroshima bomb: 100000 dead but estimates wildly vary).
However I think that if WMD were not activated at a distance, if the immediate connection between opening a bomb hatch and the resulting killing could be witnessed, then WMD would not be deployed as they have been. Imagine having to achieve the same mortality figures if each life had to be taken by slitting the throat of the victims. It is not simply that it would take more time: it would be viscerally opposed by our human empathy.
Of course, war warps our human empathy. To be successful in war, military commanders have to force their troops to carry out actions that in peace-time they would not consider. That is one of the reasons why very strict disciplines are practised. And it must be one the reasons why, when the conflict is over, so many returning war heros are deeply traumatised (for example, in 2012, more US serving troops committed suicide than died in war action).
So there is the thesis: we are more leery about pushing a fat man off the bridge because it is more "hands-on" than pulling a lever, and this is for same empathetic reason that we would be more leery of knifing a civilian rather than bombing them.
In my opinion this human empathy is embedded in our brains. Examples of its functioning exist in all areas of our society. For example, it is a common phenomenon that when two individuals of different nationalities, skin colour, or political persuasion get to know each other they often overcome antipathies they might have felt towards one another before their empathetic sense was triggered. This all suggests that our human society should become more harmonious the more we trigger our empathetic response - and this means that, as far as possible, we should engage with those we find the most at odds with our own predispositions.