“In human evolution, no inhibitory mechanisms preventing sudden manslaughter were necessary, because quick killing was impossible anyhow; the potential victim had plenty of opportunity to elicit the pity of the aggressor by submissive gestures and appeasing attitudes. No selection pressure arose in the pre-history of mankind to breed inhibitory mechanisms preventing the killing of con-specifics until, all of a sudden, the invention of artificial weapons upset the equilibrium of killing potential and social inhibitions….
But whatever man’s innate norms of social behaviour may have been, they were bound to be thrown out of gear by the invention of weapons. If humanity survived, as after all it did, it never achieved security from the danger of self-destruction. If moral responsibility and unwillingness to kill have indubitably increased, the ease and emotional impunity of killing have increased at the same rate. The distance at which all shooting weapons take effect screens the killer against the stimulus situation which would otherwise activate their killing inhibitions”. This was made disastrously worse by the use of remote-controlled weapons (such as aerial bombing, nuclear warfare, etc.).
Konrad Lorenz (1963).