You make it sound like folks had a choice.

Of course they had a choice. They could choose to become violent enforcers of the empire's will, or suffer state violence a thousand times milder than what they were being asked to commit. It's not like they were being black bagged and dragged to the front to be thrown into a meatgrinder without training or equipment, like Ukraine has been doing. They were told "go and murder for our vanity, for our dominion over all things, or sit in this box for a few years" and they chose to go do violence and bring horror and death to innocent people on the other side of the world instead of sitting in a cage for a few years.