Burning corpses and mutilating bodies aren't quite the same.
Taking souvenir ears, fingers, etc hurts the living takers more than the dead. Young men whose leaders allow them to pose corpses, mutilate them, chase each other with the parts, etc end up getting a bit metally twisted.
Depends on why you are burning the corpses. If you are doing it for fun or to release anger it is the same as mutilating a body.
Wowo we went from burning corpses to taking souveniers.