I am talking about a single action. Not multiple actions, just to clarify. What is single-handedly the most evil thing one can do? Also, to clarify... Genocide is a multi-action, therefor disqualified from this (and similar actions). Since humans, have arguable differences in morality... I want to know what people consider the single greatest act of evil... of all time.
For me... its arguably getting someone else to commit an evil act for you. Corruption of an individual. Even more so, if you convince said individual that the action they are doing is for "Good".
Thoughts and opinions are all welcome.
The co-option of others in an atrocity is interesting.
There is an RPG called Tyranny developed by Obsidian Entertainment on Steam. The main premise of the story and the game is that this is a world where a tyrant is victorious and has already won. But life doesn't necessarily stop when something evil wins, it can simply continue in that new direction.
In the story there are a few factions you can join, the one most relevant here is the Scarlet Chorus. What the Chorus does is roll up to a town, butcher everyone who resists, and then corrals everyone else into a big group and gives them a bunch of weapons. The implication is clear and obvious: you must kill those around you to survive.
In this way, people can end up killing their own loved ones, children, spouses, siblings, friends etc... by exploitation of an individual's form of survival instinct. Taking the most immediate instincts and creating an environment where there is no time, but lots of pressure, to make a quick decision about one's own survival. It is designed to bring out the worst aspects of human nature and cognition. You cannot stop the immediate from happening if you are given no mental space to even consider what is happening.
This then allows them to be co-opted into the Chorus and you often get people who, having actually found out they were willing to kill those they thought they loved the most in order to survive, are also quite willing to throw their lives away in war and battle after such a strong moral transgression and the despair that can bring.
It's an interesting, albeit not the most original (history can speak for that), version of the evils of corrupting others.