I worked in nursing homes for twenty years prior to going to school. I saw a lot of death. You always take it seriously; you just develop a barrier between you and it. You have to or you can't deal with it. What appears to be insensitivity is nothing more than a way to insulate yourself against the continual contact with loss of life. We care. We just deal with it differently.
I know a surgical orderly who is pretty de-sensitised to death. They joke around at work, amongst the corpses.
I've seen my fair share of dead bodies as well as people who have as well. Many such people may seem not to take it or much else seriously but it is often a defence mechanism (for example I'm known for always have a smile on my face and to be joking around, but inside my head something very different is going on).
I've only seen one. He was my surrogate brother... I saw him die. I was very down to business about doing what needed done. I don't ever act sensitive to it around other people, but when I'm all alone in the bottom of a bottle, I cry like a baby.