When someone has comitted a crime, society demands that they pay a debt. The debt in this case is prison time. However, after that debt has been paid, its no longer fair to deny these people their rights. They have served their time, paid their debt, and their rights should be reinstated.
If you commit a crime and go to jail, you essentially pay for the act that you committed with years of your life. To continue punishing a person like this after they have already been punished is bad for the person and bad for society in general. Most people deserve multiple chances.
I think they should. The whole concept of having served your sentence is that you have 'done your time' and are a full member of the public again. Ex convicts have as much stake in the future of their country as any other citizen, so they should be allowed to have a say via voting.
As citizens, we have the right, and really, the duty to participate in our government. Once criminals have served their sentences and been deemed "rehabilitated" they should hopefully be able to rejoin society. Once a former criminal has rejoined society, he or she should be able to regain the right to vote.
One of the lesser-known scandals in America is how many states take away the right of criminals - even those who have served their time - to vote. All citizens should be able to participate in democracy, and this is no less true for people in prison. All criminals should be allowed to vote.