Soda firmly believed that "if you don't have anything, you end up like Dallas" (176). He says this to Ponyboy to encourage his brothers to stick together and not fight so much. He uses Dally as an example, because Dally felt like he did not have anyone to rely on or depend upon, which resulted in him developing a tough, cold exterior. Dally's lonely existence had made him hard and mean, and Soda does not wish for that ever to happen to his little brother, Ponyboy. This scene at the end of The Outsiders reinforces Hinton's theme of belonging; Ponyboy and his brothers will be able to overcome their struggles as long as they continue to love and rely on each other.
Because he is rotten ans kills people.