It's worth having a look at the chapter "Sick" in "Bomb Culture" by Jeff Nuttall. He links the rise of the underground arts movement with the threat of atomic warfare. However, in the chapter "Sick", he goes further back to the horror of the First World War and argues that this type of humour is a reaction to that sort of suffering. This falls in line with what Lighter has just written in the previous post.
I read a short story by my uncle, a retired police officer, about a group of policemen who had just returned from an accident, in which a tramp had been horribly burned to death. They drove around for an hour, cracking sick puns about the burning. It was their way of trying to stop the horror from touching them too personally. I freely allow that it would have been ghastly for anyone else to have heard this.
Sick humour seems like a part of the human condition. I can quite agree we must not force it on someone who is grieving - or indeed anyone. It looks likely to be with us for some time though.