convicted criminals who serve time in jail lose most of their freedoms, for a certain period of time, as punishment for their crime. why the special concern with "the right to vote "?
however, in some states convicted criminals lose their right to vote for life! in other words, they cannot vote even after they are released back to society. this is wrong and needs to be changed; but hey, no system is perfect.

answers to Mitz Petel (PJ) & Eyal Arsi,

1. the number of would be voters that can't do so because they are convicts or ex-convicts is completely negligible. and, as PJ wrote, most poor people are not registered voters and usually don't bother to vote.
2. I really hope that one day black people in America would be considered potential voters for a democratic ticket that includes a jewish candidate for vice president.