Colin Sheridan: Reaction to Charlie Kirk's killing shows our selective compassion

A memorial for Charlie Kirk at Utah Valley University in Orem, Utah. Picture: AP Photo/Lindsey Wasson
The other night I saw footage of something that — in the annals of history — usually elicits a moniker to neatly capture its horror.
Kristallnacht, the Night of the Long Knives, even Bloody Sunday — each an example of a collective trauma so blunt, it’s etched in our memories, lest we ever forget.