Many of the states that have these laws against "felons" voting, it is often only while they are serving time or are on probation or parole.
Many people with felony convictions do not know that once they are no longer incarcerated and no long on probation or parole, they can vote just like anyone else.
I will give you that, if you violate the law, you give up most privileges, including the right to vote, but once you have paid your debt to society your privileges should be reinstated, and that should be the case in every state.
Unfortunately, things aren't really that cut-and-dried.
This is a pretty good chart that details the rules/laws regarding felony disenfranchisement. In very few states are voting rights simply restored after someone finishes their sentence, parole or probation. In most, that person has to "apply" to have their rights restored. And "applying" isn't a guarantee. Just because they ask for it doesn't mean they get it!!
Also ... it very much depends on the "crime" that the person was convicted of. For 'violent crime' felonies, most states deny the restoration of voting rights, period.
Voting Rights are Federal Law, and States are in violation of the Constitution when they make laws that bypass, usurp or overrule the Federal Law. So, most of the laws restricting voting rights of ex-felons are probably unconstitutional anyway.
Also .... this is a VERY HOTLY debated issue!! And one on which I'm not sure just where my opinion actually lies!!
Technically ... there is no "federal" or any other "right" to vote!! Which is why some refer to it as a "privilege" given to citizens and regulated by states ... because, although it's universally called/considered a "right" ... there is NO LAW in the form of a "legal authority" which really backs that up!!
Nothing in the Constitution gives any citizen the "right" to vote!! Federal and constitutional law/amendments give certain protections against discrimination when it comes to who can and cannot vote. But that is not the same thing as a "legal authorization" to perform the task of voting itself.
Initially, it was considered a "privilege" given to White men with money and power, to be able to elect a government ... which IS established in the Constitution to be a requirement of governance for the United States!! But .. the Amendments to the Constitution which cover certain rules and laws with respect to voting are simply to state that you can't leave certain people out of the process ... if they ARE indeed citizens ... with the first of them, the 14th Amendment, clarifying what a "citizen" actually is!!
The absence of federal law and the regulation of the voting process by the States is, in some arguments, what makes it a "privilege" rather than a "right." But the line is definitely blurred by the fact that it is universally CALLED a "right" even though it has NOT been LEGALLY established as one!!!
So .... I dunno what you do in a case of chaos/confusion such as that!!