Reason: Here Sam is, faced with the gut wrenching request to kill the first girl he’d really felt anything for since Jess. Dean knows full well that Sam feels as guilty about Jess’ death as if he’d killed her himself, so he slowly walks to where the two stand and, without a word, gently takes hold of his gun and slips it from Madison’s hand. It’s a silent response, but it speaks volumes of what Dean will do to protect Sam, to shield him from unnecessary pain. Sam glances up at Dean and they exchange a look. Without actually saying it, Dean’s telling Sam that he’ll do it. He’ll kill Madison and spare Sam from the horror and guilt. It’s not that Dean is willing to kill Madison because he doesn’t like her. Quite the opposite. He knows that Sam likes her and would do anything to save her. And Dean would do anything to save Sam.