One of the most enduring vignettes of the Great War comes from its first Christmas: December 1914. The Germans and British, separated by a few yards of mud on the western front, put up banners to wish each other season's greetings, sang "Silent Night" in the dark in both languages, and eventually scrambled up from their opposing trenches to play a Christmas Day football match in No Man's Land and share some German beer and English plum jam. After this Yuletide interlude, they went back to killing each other.
The many films, books, and plays inspired by that No Man's Land truce all take for granted the story's central truth: that our common humanity transcends the temporary hell of war. When the politicians and generals have done with us, those who are left will live in peace, playing footie (i.e. soccer), singing songs, as they did for a moment in the midst of carnage.
Steyn mentions the carols and the day, but misses their obvious significance. The truce didn't happen because of common humanity, but common religion. If the truce happened merely because of common humanity, then it might have occurred on any day... but it happened on Christmas Day. And they might have sung any old songs, but they sung Christmas carols.
If "common humanity" had anything to do with fostering peace, then men would not make war in the first place. Common humanity, in fact, is the primary cause - maybe the only true cause - of war, c.f. Cain and Abel.