Very simple guys, you shoot unarmed or wounded prisoners you are lowering yourself to the same level as your enemies.
Furthermore, it means that the unit concerned has cr@p discipline, at least in my humble opinion as a former lowly Lt.
Furthermore, for those of you who fly over that area, do you think your chances of surviving as a prisoner are enhanced or retarded by OUR treatment of prisoners?
Be very careful who you talk to about this stuff and don't expect any Australians to join in. One guy almost got Court Martialled for kicking a dead body in East Timor a few years ago. they take it very seriously down here.