First, citizens vote. Voting is the single activity that separates citizens from non-citizens. Citizenship may be defined as possessing the right to vote.
Convicted criminals are punished in many ways. They are fined, made to perform public service, imprisoned; we take their stuff, their time, even their freedom. But they are not deprived of their citizenship: citizenship is a birthright or, if naturalized, a well-earned and well-deserved status.
And unless we take their citizenship, as long as any person remains a citizen of this nation, they retain the right to cast their vote to determine who runs their government.
A second argument:
We have decided over the course of our history that we will not discriminate concerning the right to vote. Access to the ballot box does not depend on any property qualification, or literacy test, or poll tax, or race, or creed, or color, or gender. The ruling principle is that these requirements are discriminatory. We, as a nation, as a matter of settled law and fundamental values, do not discriminate for any reason regarding citizen access to the ballot box. All citizens shall be able to vote.
Meanwhile, the evidence seems undeniable and universally accepted that the justice system in this country is demonstrably discriminatory. Throughout the entire process, at every step from initial contact to sentencing, the data clearly show beyond dispute that wherever you look the system discriminates. It discriminates against people of color, the poor, and women: consistently, against over half our population.
Those two statements, taken together, that we do not and will not discriminate with regard to voting, and that the justice system is discriminatory, mean that we cannot use conclusions of the criminal justice system to determine access to voting rights.
Felons have the right to vote.