Honestly they should not be allowed to; you got convicted, you did the time. In the US's stupid penal system, you have paid your debt to society; in others, you (should) have rehabilitated. That's it, you do the time, clean slate, move on.

The stigma with former felons is why there's a lot of repeat offense, why people stay stuck on the social ladder, and of course why the US' attempt at democracy is laughable.