If the buck-stopping point is the Word of God being interpreted by men, that is not "Scripture interprets scripture". That is man interpreting Scripture.
A8: So why all the Protestant sects?
Dr.E: The truth is not in all of them, but it is among them. Our task is to discern it, with eyes and ears given by God for that which He has purposed from before the foundation of the world.
Notice that you didn't answer the question. Telling us that the truth is in all of them does not tell us why there are many instead of one, since (in your opinion) we do not need men or magisterium to interpret Scripture.
-A8
Telling us that the truth is in all of them
I do not believe the "truth is in all of them."
I said the truth is among the various Protestant faiths, but many are misguided or flat-out wrong.
All believers who possess Trinitarian faith in Jesus Christ as Lord and Savior are among God's elect. That faith is evidence of their salvation, not a cause of it. That's what Scripture tells us.
God's sheep are found in many disparate locations. Even among the RC church, no doubt. But I assume God will further amplify their understanding and eventually bring them into a more Scripturally-sound, Reformed Christianity.