A felon, meaning "a person who has been convicted of a serious crime" fits all the criteria for someone that forfeited their right to vote. Willingly or knowingly causing sufficient harm or even unwillingly, considering mental health issues, they would still need to be reasonably excluded from voting due to the incapability of making sane decisions. The right to vote is a very important duty and privilege for many reasons. It inherently requires restrictions.

Voting is a fundamental and important right, duty, and privilege. You would have to agree with this since you wouldn't be arguing for felons' a trivial or meaningless right. "If we want felons to re-enter society" then the correct signal to send is that actions have consequences and that "law-abiding citizens" need to follow the law. The proper reaction to "misbehaving" is correction, not enabling behavior that's detrimental to them and/or others. And, yes, "their voice doesn't count" because of their own actions. The signal that you're sending is that the people who seriously acted against the will of the people, who have disregarded most or all principles required for civilized society, and who have proven to not have basic human morality should be given the same say as law-abiding citizens and also that such a felon's vote would be helpful for the society he/she has acted on destroying. Not only is this immoral, illogical, and unfounded, but there's also the assumption that such a felon's recovery is directly linked with being able to vote. Which is, at the very least, not necessarily true. There are many legitimate reasons for a democracy to silence X people. One of them being underage people. Others being mental health issues or, in this case, people who have proven to be incompatible with civil society and basic human decency. Preventing these votes would in fact protect society. It's not a matter of "being afraid"; it's about stopping people who can act or acted for the destruction of the nation. Justice is about pursuing appropriate punishment or compensation depending on the act. Where's the justice for the law-abiding, tax-paying citizens working and striving for progress when bad actors are allowed to undermine them?

The first hypothetical that you've raised can be considered a good case for the reinstatement of the vote. However, I would still disagree for two reasons. First, it is a very small exception, and laws can't be feasibly made based on exceptions. The resources required to implement this would be disproportionate to this "better" outcome. Overspending funds that can be used to help more people supersedes this issue. Second, the "evil" acts committed don't disappear regardless of the recovery. Becoming a law-abiding, tax-paying citizen is a normal expectation, not a special achievement. It's commendable, but "rewarding" this by returning the vote would undermine the important signal that actions have consequences. And that it would also be unfair for all the "regular" citizens that don't get "rewarded" for paying taxes and don't commit crimes. So no, the commendable recovery does not supersede the crime. A government isn't supposed to be and can't be "God" capable of such forgiveness or moral judgment. Social cohesion, stability, human nature, etc., are to be balanced. "Incapable of making sane decisions" isn't complicated to understand. There are many cases of people not being allowed to drive or sign contracts, etc., for reasons under this umbrella term, such as mental health issues, serious crimes, etc. But regardless, driving, signing contracts, etc., are all examples incomparable with the the right to vote. Because they don't inherently affect millions of people and the future of the nation. You cannot reasonably make the case that voting is on the same moral, serious, and conceptual level as these other examples. It would be like saying that owning a slingshot is the same as owning a tank. The duality that you posed of "pick one" doesn't follow. There's no reason to establish or require "black and white" solutions or punishments. We can perfectly make case-by-case consequences and compensations accordingly. The law already does this. And in your case, it's not reasonable or moral to assume that just because someone stopped being a horrible human, it now clears them of all consequences. Severe actions deserve and require severe consequences. For the sake of the nation. For the sake of civil society and the will of the people.