Adding The Book of Mormon and claiming it, too, is inspired differs in magnitude but not in kind from throwing out the books of the OT. Or, is the assertion that it's OK to throw out portions of the Scripture but not to add to the Scripture?
Mormons do not believe Jesus Christ, God from God, is our risen Savior which means they are not Christian no matter what they like to call themselves. Those who today are focused on being anti-Mormon and tomorrow focused on being anti-Something else but agree with what Joseph Smith said about the Catholic Church and about Christian denominations or groups other than their own are just like Joseph Smith. They're people who have made up their own religion and claim it's Christian but who in reality are not Christian.
Excuse me? I believe that Jesus Christ is my Savior, that he died on the cross and was resurrected 3 days later. He dies for my sins, for all sins committed by those who lived and live on this earth. And I am a member of the Church of Jesus Christ of Latter-Day Saints. At the judgement day Christ will look upon my heart and see how I followed Him and his words and teachings. That is what it all comes down to for everyone.