They forfeited that right when they were convicted and sentenced. As for the “they’ve paid their debt to society” BS, yes they have but permanent forfeiture of certain rights is part of the “debt.”
That’s a double edged sword, if you put someone back out in society hamstrung with the permanent disability of abridged rights and privledges there’s a large incentive, particularly from an employability standpoint, to commit crime to make any financial headway. If they have some level of hope that life can be normal it goes a long way to keeping them on the straight path.
No, punishment that goes beyond the sentence served is not part of the sentence. Restoration of rights should follow paying one’s debt.