you know, given the size of the incarceration rate in the united states, allowing prisoners to vote could seriously swing a few elections. there are some difficulties, though.
let's say you commit a crime in new york city, and get sent to a penitentiary upstate. you would still be in the same state, even if municipal elections are a somewhat tricky jurisdictional concern. but, let us suppose that you have a residence in california, you are arrested in new jersey for a crime you committed in new york, and are sent to a locked down correctional facility in new hampshire. where do you vote?
the jurisdiction is important, as there would be some likelihood of the inmates of a large jail assuming political control over rural counties, should the number of inmates outnumber the number of residents in the region - a scenario that nobody would find acceptable. and, what if the result of some controversial referendum is close enough that the number of inmates voting is an effective swing? what if a referendum on gun control is successively blocked by the margin of the inmate population?
i believe in a concept of citizenship. while it is best to maximize the scope of voting rights, it should always be done with an eye towards the parallel expansion of citizenship obligations. incarceration is the temporary cessation of both your rights and your obligations as a citizen, and there is consequently some ground for restricting the franchise to those who are actively incarcerated. i would rather meet the debate at the door and instead propose that any restrictions on voting rights due to prior convictions should be entirely abolished.
if one is concerned about voting rights for the incarcerated, it would perhaps be more productive to pursue policies designed to reduce the size of the prison population than an expansion of the vote to the incarcerated population.
a vote from behind bars is always going to be an act of absurdity.