Pride
Pride goeth before destruction, and an haughty spirit before a fall.
I had a federal drug conspiracy sentencing this week in which I was arguing, based on my client's horrible childhood and his history of being a law-abiding and productive member of society for all but two of his 49 years, that he should not go to prison.
The government's argument was, "there are lots of people who have horrible childhoods and don't commit crimes." My response was, "show me one person who, when he was six, saw his mother executed by his father and who, at age 10, was present when his cousin murdered his father, who didn't get tens of thousands of dollars of therapy, and who didn't wind up breaking the law."
But this didn't get through to the prosecutor at all. Because really the "lots of people go through the same things and don't break the law" argument isn't about real human beings experiencing horrible trauma, neglect, and genetic misfortune. It is, rather, about the prosecutor imagining that he would have done better if he were in the defendant's shoes, just as a good defense is about convincing a jury that they might have done the same in the accused's shoes.
Because, really, how severely can we punish someone for something that we would have done in the same circumstances?
"The same circumstances" have to include not only the specific traumatic events, but also the rest of the defendant's upbringing, as well as his genetic makeup. Human behavior is incredibly sensitive to initial conditions, and nobody can say what single genetic switch might make the difference between a Hitler and a Schweitzer.
If a prosecutor had the same genes as the defendant and the same upbringing, he would be the defendant. The proposition, "I would have done differently in the same circumstances" is prideful. To say that you would, if you were the same person, have acted differently is to claim that there is something special about you that could overcome the nature and nurture that the defendant couldn't conquer.
Pride used to be the Seventh Deadly Sin; it got Lucifer cast out of heaven; now it's a prerequisite for public service.