I could never work in research, take a biology disecting class, or live on a working livestock farm.

Yes at work we do surgery and all manner of gross stuff to animals at work, but the animals are asleep, and what we're doing to them helps them, not destroys them (well save for euthenasia but that's usually a blessing to end horrible suffering). When we're done with an animal it wakes up, and usually feels better either immediately or in a couple days and you can see it's health improve. Somehow that makes what we do easier to deal with.