Unbiblical or unscriptural does mean "wrong" if one considers the Bible to be the authoritative word of God.
LDS indeed "don't" consider the Bible to be the authoritative word of God, we consider the Word of God to be the Word of God, in which the Bible also contains. We are not Bible "idol" worshipers.
The fact that Latter Day Saints claim without basis that the Bible has been corrupted and instead turned to man-made "Scripture" to formulate a man made religion does not make them right it makes them apostate.
1. "Without basis"....? Be careful of your words. We don't believe anything without basis.
2. LDS do not consider ANY scripture to be perfect. Even the Book of Mormon Joseph said it was the "most correct" book, because it was pure revelation and hadn't been in mans hands much to mess much up. But even it he didn't say was "perfect".
3. LDS recognizing that men with their own designs over 2,000 years both compiled what was an wasn't scripture (several times mind you, adding and removing things), and the many translations, and we know things are missing, etc. etc. Doesn't mean LDS don't consider the Bible to also contain the word of God. Heck, just translation alone, which translation is the "true" translation? Especially the modern ones? I've seen specific examples of how the NIV the most popular Evangelical version corrects some things, but entirely perverts others, and even inserts Evangelical interpretation into the Word. Which Bible? The Orthodox Bible, the Catholic Bible, the Protestant Bible??? You do know each one has different books of scriptures etc. in them??? So get off your high horse that LDS actually know the Bible for as it is.... It is the Word of God and the Correct Interpretation of it that is Key. It as a book is not "divine".
4. Revelation from God is not "man-made". Just because YOU have been told to believe in the man-made doctrine that there will never be revelation, scripture, etc. again, doesn't make it true. The Bible doesn't say that anywhere, yet you choose to believe that man-made doctrine.
The Jehovah's Witnesses at least adhere to God's Word. Even though they've come up with a number of unsound doctrines there is at least the possibility so long as the Bible remains the cornerstone of their faith that the Holy Spirit may draw them into the fold.
Let me tell you a little secret.... Mormons also use the Bible as a stone in our Faith. In fact, of the 4 years of our Sunday School scripture rotation we spent 2 years on the Bible. Have you even ever stepped into an LDS Church to even know what you are talking about? Clearly you haven't.
We don't have any "lessons" saying what is and isn't "corrupt" with the Bible.
The Bible is equal, hand in hand with our other scripture.
We study the Bible just as anyone studies the Bible.
There is nothing in Mormonism that conflicts with the Bible, if it did, we wouldn't be mormon. Further, me as a convert to mormonism, I know for a fact it doesn't conflict. But I also know that all your religions DO in fact conflict with it. I spent years in your religions, being beholden to NONE of their biases and interpretations. I just read the book for myself. And because of being in so many of your religions, it was easy to see all the man-made interpretations, the omissions, the perversions, etc. Only when I later came upon Mormonism did a religion in FULL and Accurately fit what the Book in Full said.
The Mormons? So long as they don't consider the Bible to be the cornerstone of their faith it isn't nearly as likely.
All scripture and truth is the cornerstone of our Faith, and Jesus Christ is the CHIEF Cornerstone....