For centuries people have sought to hold onto something from their relatives. Before photography, this took the form of death masks (made from plaster of Paris) and cuttings of hair. Death photography was a natural extension of this practice. For some people, having a picture of a dead relative might help them through the various stages of the grief process.
Not in the least! Once I lose a relative, I no longer view their body as being them. It is simply a corpse, no more and no less, so if people wish to photograph it then I have no objection.
It is not a good practice taking pictures of sad moments. Generally people take pictures during happy occassions. My personal openion is more or less similar to yours.