Certain persons on the Forum have stated that Massena issued orders to prevent the kind of devastation you have admirably summed up but those orders have never been reproduced on the Forum, although frequent mention is made of them.
A few days ago I cited the relevant basis of French military law during the period, the Code Militaire and the Code Penal, the first of which forbids the mistreatment of civilians and the second of which authorizes penalties up to and including capital punishment for soldiers found guilty of such offences. Clearly, the French were not enforcing their own military law.
The question is why weren't they?
dg