Good question….very difficult to answer. I believe that if you are currently in prison, you should lose some rights and not be allowed to vote.
I have personally seen many people in the last presidential election who had no F clue what the candidates stood for and voted based on ideals rather than facts (or lack of facts) and now are asking themselves why their candidate is doing what he is doing. In retrospect, it seems that these voters were not sufficiently informed to know what they were choosing (or didn’t care). Ideally, these would be the voters to weed out or educate them on the issues more. That, however, is impractical and impossible.
The legal arguments about who to include and who to exclude would never be resolved. Maybe you could have a written test about the issues and each candidates platform – and if you get a 90% or above, you prove that you know what you are voting for and would be allowed to vote. Who would write the questions? How would you choose what a passing grade is? Obviously, you would have to have people helping illiterate people take the test by reading it to them. You see, the ACLU would have a field day, the whole issue would be locked up in dispute, and it would not be allowed to happen. But I can dream…....