If people heeded John 17 and 1 Corinthians 1:10, it would be clearer to the world whois a Christian and who is not. But, we live in a time of religous Babylon, where men build their own way, rather than being One Church as in the Bible.
And that is where LDS and many other false teachers fail.
The Church of Christ is the body of mankind, the world over, who have accepted JC as their Lord and Savior.
All Christians comprise the the church. Not some particular dogma, faith, cult or system.