The key phrase being "without due process of law."
Disenfranchising convicted felons no more violates the 14th Amendment then imprisoning them does. I would say that the right not to be locked up in a room for years is a far more fundamental right than the right to vote.
Exactly.
Actually it does — because the law is not valid.
That's right, it is a legal non-entity.
Why?
The Constitution speciffically prohibits laws of an Ex Post Facto nature to both the federal government and the states; even with the Supreme Courts considering this restriction only upon criminal laws, that this increased the punishments of those already tried and convected makes it ex post facto.