You're walking past a duck pond. In the pond, a child is drowning. You have the power to save him. There are twenty people sitting on the bank doing nothing about it, and you fail to swim in and save him. If he drowns, you've done a bad thing.
OK, most metaphors fall to pieces in the end, but this one never gets together in the first place. I suggest that slightly more robust, though clearly not invulnerable, is:
There is a prison which we helped to set up and staff. Over the years a régime of bullying and even lethal abuse emerged. At first we encouraged it. Then the prison governor gave some friends of ours a kicking. We stormed the prison and killed some of the prisoners. Then we withdrew, leaving the prison governor in charge, but we put the prison on short rations, which the prisoners had to pay for through the nose. The young and weak died in significant numbers.
The bullying continued, got worse, and to stop it we occasionally flew over the prison and bombed it. Tales of lethal substances inside were rife, though, apart from stuff we had helped the governor to procure, not substantiated.
Ten years after we gave the governor his first kicking we decided to go and give him another, even bigger one, kill a lot more prisoners, steal as much stuff as we could, trash the prison infrastructure, and liberalise the prison régime by handing over power to a group of conflicting prisoners’ councils.
Despite the resilience and good will of a majority of the prisoners throughout this time, parts of the prison descended into non-stop, high casualty rioting, and the infrastructure deteriorated even more. The bullying did not stop.
We started to talk about leaving the prisoners to their own devices and going and kicking the shit out of another prison next door.