I'll kill sims if the story demands it. Or the house needs room for the next generation and the sim has stopped being fun to play. It's not something I enjoy, but it's not something I specifically don't like doing either. But it is rare that I need to kill them, and most die of old age (or occasionally exposure/stupidity because they decide that going swimming during a blizzard in Brindleton Bay is the right way to deal with their hygiene need...)