The subjective sense of cuteness.
It reminds me of the furor over slaughtering harp seal pups in 1970s Canada. We react in horror to killing mammals with those big, cute eyes while girding up with paper napkins in anticipation of eating the lobster that screams as it is put alive into boiling water. It was said to be a mammal chauvinist thing, but that rationale fails on the horsie level.