Why are the most fun things in life only great fun if you lack compassion?

Years ago, when I was still living there, my father put up a martin house visible from the family room and vigilantly guarded it against squirrel squatters. He would sit in his recliner six feet from the patio door, open the screen about one inch, and keep a pellet gun at the ready. The gunshots wouldn't really injure the squirrels, but they sure annoyed them.