I missed your note about what Madison put in the Constitution to protect the sufferage in the Senate does not matter. I guess that says it all about your view of the Constitution. This was the only subject requiring unanimous consent and it does not matter.
You might want to read up on the 17th. There were a lot of good reasons for passing it at the time, and by the time of its passage, most states had, on their own, gone to a form of direct election.