...low effort high gain, the same for any other situation...
I am assuming this refers to the act itself, since there is no way to quantify mental activity in terms of energy cost.
According to this, if an oil company wanted to make a pipeline through a village in Africa, it would be best for them to just exterminate the village rather than relocate it; dig a hole and dump all the corpses.
It would mean higher gain, as fewer resources were spent to obtain the goal, rather than if they had to spend resources on relocating the village or building the pipeline around it.
And for the villagers, the act of dying is certainly less costly in energy than moving the entire village.
Win, win, so the mass murder turned out to be a morally good act... Is that what you are saying?