The idea of prisoners voting is contrary to common sense and the Catholic tradition of penance prior to redemption, but it still struggles to become normative, per this article from The Economist.
An excerpt.
“MOST rich democracies spend a lot of time and money trying to convince more people to exercise their right to vote. So it might seem strange that some of the same countries take some trouble preventing thousands of citizens from going to the polls. In 48 American states and seven European countries, including Britain, prisoners are forbidden from voting in elections. Many more countries impose partial voting bans (applying only to prisoners serving long sentences, for instance). And in ten American states some criminals are stripped of the vote for life, even after their release.
“There is scant public sympathy for characters such as Peter Chester, a British child-killer whose bid to use human-rights legislation to win the right to vote from his cell was rejected on October 28th. But voting should not require a character test. The punishment of monsters such as Mr Chester consists of the prolonged deprivation of liberty. Withdrawing the vote from them only hammers home what they already believe: that normal social rules do not apply to them.”