I'm ok with people serving time (including parole) being restricted from voting. We curtail many rights and freedoms people are normally entitled to as part of incarceration, including behaviors which are vital to a healthy democracy, like protest. I'm ok with prison not being a valid legal residence for registration purposes or a location for a polling place or voting booths for secret ballots. That also DOES strike me as a context ripe for illegal intimidation & fraud, engaged in by prison officials. Once their sentence is up, though, there is absolutely no basis for further disenfranchising them. They've served their sentence, voting isn't a recidivist behavior or temptation, and it poses no direct threat to anyone else.
(and no, Lewk, I do not in fact approve of things like Megan's Law, nor do I approve of a criminal record as grounds for restricting firearms ownership under the current framework and context)