"He doesn't really care about anything anymore" is the end result. I've seen one soldier tantrum with with this trait, the only survivor of a full tantrum spiral who survived with about 8 happiness and quickly recovered.
Truth be told, this is a highly desirable trait, and seems to be encouraged by witnessing violent death (not butcher shop). There have been many attempts at recreating this trait in a controlled environment, including babyfalls, automatic puppy droppers, controlled siege eradication, and abuse of pets and danger rooms.
I can't find the thread right now, but there's a great method for violent death farming. Build a room way up, far enough for a lethal fall of whatever animal you're using. Punch a few holes in the floor, and cover them with hatches. Then place pressure plates around the room, linked to the hatches. Place female animals in this enclosure, and leave the males secure elsewhere. The effect is that the females breed, and walk. As they walk, they hit the plates, and a hatch opens. At low population, this is rare, but as population rises, the chances grow, and it's much more likely for something to be standing on that hatch. Thus, the population in the room is never zero, but it fluctuates at some limit according to room size and hatch number. There should be a roughly consistent stream of falling animals after a while. Place this in your dining hall or barracks, and your dwarves will be exposed to falling animals on a regular basis, letting them experience death and grow hardened.
Perform this with wild animals, and you can butcher the remains. Do it with domestics, and they cannot be butchered. Cage traps should help you get some good, non-grazing animals, like lions or or something. With sufficient dwarf power, you could even modify this for aquatic creatures, and use carp for added dwarf, or whales for added food.