I always thought it went hand in hand with the people who don't want bad things happening to kids, something to do with them going in the, "Protect the helpless," section of some people's hindbrain. Usually I only see it applied to pet-type animals, considering your average person gives zero fucks about where and how our food is made. Kick a puppy? Monster. The average living conditions of chickens? Who cares so long as the food's cheap.