To a great extent, we have distanced soldiers from the carnage -- which makes it so much easier to go to war. Wikipedia on the Christmas Truce of 2014:
Although the popular tendency has been to see the December 1914 Christmas Truces as unique and therefore of romantic rather than political significance, they have also been interpreted as part of the widespread non-cooperation with the war spirit and conduct by serving soldiers. In his book on trench warfare, historian Tony Ashworth describes what he calls the 'live and let live system.' Complicated local truces and agreements not to fire at each other were developed by men along the front throughout the war. These often began with agreement not to attack each other at tea, meal or washing times, and in some places became so developed that whole sections of the front would see few casualties for extended periods of time. This system, Ashworth argues, 'gave soldiers some control over the conditions of their existence.' The December 1914 Christmas Truces then can be seen as not unique, but as the most dramatic example of non-cooperation with the war spirit that included refusal to fight, unofficial truces, mutinies, strikes, and peace protests.