First, the whole argument ignores general equilibrium effects. When women got the vote, party platforms changed. The system is designed to push the parties to the "center". When you change the electorate, you change the center, but you do not change the incentives.
Second, I am irritated by this line of reasoning,
"Ex-felons (that is, former offenders who are out of prison and who have served parole and probation) in 12 states lose the right to vote permanently despite paying their "debt to society"."A different, and correct, way to say this is that 12 states have defined "paying their `debt to society'" to include not voting.
Finally, when I ponder felons voting, staunch opposition to requiring voters to show ID, and eliminating secret ballots in union elections ("card check") I have to wonder: is this really the best the minds of the left can come up with? All three initiatives seem both politically tone deaf and unlikely to do much good, other than for democrat politicians. How about advocating for something that would actually help the poor, like marijuana legalization? A lot of those felons are felons solely because the saints among us cannot abide the thought of the evil weed. How about a negative income tax? How about school vouchers? How about fewer wars? Yikes.