In Nuremberg we developed a way to think about this: people outside the central circles of power have a tremendous amount of pressures they are considering. It's definitely the case that some are sadistic and horrible, but more are just following orders and trying to get by as best they can, and punishing them for war crimes is not appropriate.
The other side of that coin is that it isn't realistic to expect soldiery en masse to resist illegal orders. It's always more complicated than that.