@1234muse we saw armed insurgents execute pro-Empire prisoners and civilians, that's a fact. We saw civilians rebelling and starting riots, that's also a fact.
Was it stated anywhere that half of the population (in any large city that would be an
enormous number) was made up of armed insurgents? Was it stated anywhere that they were going to kill
the entire other half of the population? Did we even see the insurgents carry out a massacre on that scale?
No, nowhere.
Exaggerations and assumptions like those are incredibly dangerous, and have led to horrific events in real life. Innocent lives were already being taken in Arene, but The Empire turned it into a full-scale massacre, killing anyone who remained in the city center indiscriminately. It was a cold, rational decision from their point of view, minimizing their own losses while protecting their war effort. But from a moral point of view, it was a disproportional response unlike anything The Empire had carried out before.
Proportionality is considered carefully in modern, real-life warfare today. If you read the news, you probably know about the recent incident where Iran shot down an unmanned US drone. The US considered a large-scale counterattack, but ultimately decided against it, since killing dozens (or maybe even hundreds) of humans was seen as a disproportional response to a shot-down flying robot.