Then why release them as citizens? If you dont trust them to be able to handle their rights, then you should not release them. If the punishment is meted out by the judge or jury, why does a parole board (not mentioned in the Constitution) get to add additional punishments upon release?
Release conditions aren't additional punishment. If the law states, "Felons cannot own or possess firearms.", it is clearly an original sentence from being found guilty. A lifeling sentence of lost rights (voting, firearms) and a defined sentence of confinement. You are arguing that it must all or nothing, but that is not the law, nor logical. You can argue for life sentences for all felonies if you like, but that is a different subject.