A few more:
So a businessman is searching for love, and despite being able to choose practically anybody he wants due to his vast wealth, he picks the most messed up, abused, physically scarred, sociopathic basket case imaginable, who drugs him, stabs him in the eyes with needles, makes fun of his chin, cuts off his feet, and intends to keep him in a sack living off regurgitated vomit, although she is quite pretty.
So the reason he was kidnapped and locked away for 15 years and then decided to hit people with hammers and eat a live octopus upon release is because as a teenager he witnessed another kid fucking his own sister.
And one courtesy of Christopher Hitchens, just because it's my favourite sentence in the world:
So we'll pick the most backward, the most barbaric, the most illiterate, the most superstitious and the most savage people we can find, in the most stony area of the world - we won't appear to the Chinese, who can already read - we'll appear to this brutal, enslaved, hopeless, superstitious crowd and we'll force them to cut their way through all of their neighbours with slaughter, genocide and racism, and settle on the only part of the Middle East where there's no oil; and without this we wouldn't know right from wrong.