Felons, once they have served their sentence, have repaid their debt to their community in the eyes of the law. There is no reason to continually punish them, especially when it blocks their progress in reintegrating themselves into society and discourages them from becoming invested in the community.
This argument also assumes that felons are beyond change. It argues that because felons disregarded their community's wellbeing in the past, they will retain their disregard for the rest of their lives. Felons are capable of becoming upstanding citizens and leaving their past behind.