People in prison in the United States should be given the right to vote. They are still citizens of the United States of America, regardless of the fact that they committed a crime, and whoever the rest of the population votes for affects them as well, regardless of the fact that they were not given the chance to vote. And what about when they are released? The weren't given the opportunity to vote when they were in prison, yet now they still must live by their rules.
People in prison are there because they committed a crime; it is punishment. They have gone against DIRECT LAWS made by the United States of America, or laws made by the state in which they live, which is why they are in prison. If someone wilfully disobeys a law and are put in prison, they should not be able to vote because they disobeyed the very government they are voting for. Would you say that someone who tried to assassinate the President should be able to vote? Of course not.
What about when they get released? If someone was in prison during the presidential election, he could not vote for his choice. Once he is released, he would still have to abide by all laws passed by the president even though he was not given the chance to vote for his choice. You said that if someone assassinated the President, they shouldn't be allowed to vote. Of course not! But ot all crimes are as severe as that. And if they were wrongly accused? No one should be denied the right to vote.