When I was in college I worked in a lab where part of my job was killing rats (I actually had a real moral problem that the general term used for the killing of lab animals at this time was "sacrificing", e.g. "I sac'ed that litter of rats yesterday", because it felt like a way to lessen ones natural emotional guilt at the task. Not sure if that term is still used today.) I really had a moral quandary in what I did, even moreso because I felt a visceral disgust (like I actually threw up a bit) the first time I had to kill a rat and then cut off its head with a pair of scissors, but after I got used to it I had no problem with it - I came to understand how people can get used to doing things they originally found morally reprehensible, and it scared me about myself.

Anyway, I always found my guilt was assuaged at least a little bit if a mama rat would eat one of the babies by herself. "Hey, I'm no worse than the mom!" I'd say to myself. Then I felt a lot worse when I came to understand that moms tend to eat their babies when under high stress or when they think a baby is sick, which was probably a result of living in the lab in the first place.