While all armies behaved badly at times, I think the reason the argument focuses on the French armies is because they spent so much time in countries where the population was unsupportive that their behaviour towards civilians becomes more conspicuous.
As far as I can make out, ever since Custine went into Frankfurt in 1792, French armies that went into foreign territories as 'liberators' left them with wagons of loot and the curses of the population. Orders from on high to repress dissent with violence did not help.

regards,

Susan