Jail time is punishment for crimes--once jail time is over, a person is supposed to begin a new rehabilitated life. This sort of ban-the-felon-from-voting is an ever-lasting an unfounded form of moralistic judgment that mirrors The Scarlet Letter: let's punish all "sinners" forever and ever and make them social outcasts.
Psychologically, this does not make any sense either. If you treat someone like a criminal forever, it only encourages that person to behave like a criminal.
Anyhow, check out the full article here.