The whole idea of "register to vote" is, IMHO, a scam meant to reduce the number of voters.
That's pretty obvious. Maybe it wasn't intended as such, but it is quite convenient for the existing political class. I never understood why there is no broad movement against this in the US.
There is a very good reason for that, back in the early 1900's voter registration did not exist. If a dirty politician wanted to win an election he simply had his friend from the army bring the soldiers he commanded to go vote on the day of election. Registration is used to ensure things like this don't happen, verifying residency is now possible because of registration.
There are two issues with voter registration: First, it creates an obstacle to voting. If voting requires 2 steps, fewer people will vote. Second, (if I understood this correctly; forgive me if I didn't, I don't live in the US) you must publicly register for a party. In other words, voting is not secret. Secret elections areis a prerequisite for democracy). Here in Germany everybody is registered anyway. You might find this problematic for some reason or the other, but at least it ensures that everybody is registered to vote excatly once.
Another thing which disturbs me about the US presidential elections is the winner-takes-all system for a state's members of the electoral committee. This essentially ensures that democrats and republicans remain the only parties, because it makes it hard for a smaller party to win even a small number of seats in the electoral committee. In some cases, running for president even helps the political opponent: In 2000, the votes cast for Ralph Nader who is (arguably) politically closer to the democrats, made Al Gore (arguably) lose Florida, which led to GW Bush's victory.