what should the penalty have been for Hester's crime

Puritans often had different punishments depending on the person and severity of the crime. Hester's punishment was pretty standard. They liked to humiliate the person publicly. Branding Hester with a scarlet letter meant much gossip and condemnation to be had over an extended period. The hypocrisy in the village is evident and people like Hester are made scapegoats for their own secret sins.