What is a good scapegoat in the story "The Outcasts of Poker Flat"?
The better question is 'who' serves as a scapegoat in the story. A scapegoat is someone who takes all the blame even though he/she is innocent. The term has its roots in Bible times where the Jewish priests would lay their hands on a goat, transferring the sins and guilt of the people onto the goat. Then the 'innocent' goat was led out of town and killed.
The outcasts in this story who are 'led' out of town, serve as the scapegoat for the town of Poker Flat. At the beginning of the story, the reader is told that the town had recently experienced a rash of crime. The town was a wild west town known for criminal activity, but it had gotten worse than usual so the lead townspeople got together to figure out who was to blame. They weren't really looking for the truly guilty persons; instead they just wanted to find someone to punish, hoping that other criminals would see the punishment and be scared into submission and reasonable behavior.
The outcasts of the story are the people that the town decides are 'guilty'. Their punishment is to be banished from the town. If they return, they will be sentenced to death. In this way, they serve as a scapegoat for the townspeople who just want someone to blame.