The source of human conflict

I agree that part of the problem does lie in the manner in which the human brain evolved. The most primitive ("lizard") parts thereof are designed to react in a reflexive, often violent manner to perceived, existential threats. These responses are often excellent for the short-term survival of the individual, but may not be so good for the long-term survival prospects of the species. Humans are capable of amazing creativity, great benevolence and impeccably logical philosophy. The problem is, when faced with a mortal threat, one must first survive the moment before any of those products of higher mental function can begin to come into play.

A few other random considerations which may pertain:

•I once read in some book about early childhood development that said a person's ability/tendency to empathize with other people arises at a pretty early age.  If that developmental "window" is missed, all else being equal, the person will tend to be less likely to consider the feelings/best interests of others into his/her future decision-making processes.

•A vicious thug with a weapon will generally be the sole survivor of a one-on-one confrontation with a benevolent pacifist.

•From the individual's point of view, our species is the product of a pretty brutal ecosystem.  We have existed through time as both predator and prey.  Our hunter-gatherer ancestors were no doubt keen observers of the real-life dramas they witnessed on a daily basis.   This ongoing battle for survival taught them that strength, cunning and a willingness to kill generally had higher survival value than fairness and sentimentality.  If you watch predators in the wild (rather than just in Disney cartoons) you learn pretty quickly that they often start eating their prey while it is still alive: not a lot of empathy, there.  Many young prey animals learn to stand and even run within an hour of having been born for good reason: their lives depend on it.  Nature is indeed "red in tooth and claw".

•For our ancestors, living by their wits out on the plain, the burning question was, "how can I stay alive til tomorrow...or even for the next 5 minutes?", not "what course of action would be in the best interest of the long-term survival of both my species and the planet?".  The conundrum arises from the fact that we evolved to find an answer to the first question, not the second, and that the answers to the two questions are often not the same.