I would put it this way:
"Morality" is an abstract noun, and like many abstract nouns, can not be found in nature. You can't go to the back garden or down a mine shaft and dig up a lump of morality.
Morality is a concept invented by humans that exists only in the mind of one or more humans. It happens to be a very useful concept, but that is beside the point. It follows that the boundaries of morality are defined not by the concept itself, but by what the relevant human mind decides are the boundaries.
There is no absolute morality. To imply otherwise is to misunderstand the word.