Ummm....Gal 1:8 for starters?
The LDS and JWs have the same thing in common as virtually all other cults: they appeal to an authority outside the Scriptures for their doctrine. The LDS have other scriptures written by their false prophets Joseph Smith and Brigham Young. For the JWs, founder Charles Taze Russell claimed that only he could rightly interpret the Scriptures. Like other cults, they have fundamentally flawed Christology and soteriology, denying the true deity of Christ and relying upon works for salvation.
I realize you are attempting a reductio ad absurdum argument here, but lumping Protestants and LDS/JWs together is so inappropriate (and unfortunately, so frequent) that if it keeps up we just may need yet another corollary to Godwin's Law.
And they will tell you that the Bible does not say "right theology" saves you. Belief that Jesus is the Messiah does.
I stand ready!