Demons were a species a bit different from humans. While humans didn't allow their instincts to guide them, the demons did the opposite. They followed their instincts as if it was natural and it probably was, if not, then there wouldn't be humans that acted worse than demons if they know that they could get away with their actions.
Of course, it didn't mean that humans were bad, the same goes for demons. Even if their instincts made them bloodthirsty and ruthless, they weren't necessarily bad, atleast from their point of view.
But that also didn't mean that humans should stop fighting against them. They had to fight if they wanted to survive. It was to devour or get devoured and the Empress knew that well, very well.
That's why when a Magus of hers decided to attack a city for his personal grudge, she didn't stop him. Instead, she used it as a chance to make a power move, to break the stalemate.
Destroying a city wasn't enough, she needed more, and she will get more!