Introduction - The Seventh Day Adventist Church - Cult or Christian?
Many Christians, even Christian scholars, believe the Seventh Day Adventist Church to be a cult. The word usually applied to religious groups that claim to be Christian, but follow the personal interpretation of one or more individuals, rather than the understanding of the Bible accepted by mainstream Christianity. In other words, most Christians arrive at their conclusions based on whether or not these groups are "orthodox" ie. they conform to the traditional or generally accepted beliefs.
The word "heresy' usually gets the same treatment. For example, Greg Koukl says a heresy is
This leads me to wonder whether Greg Koukl believes that "the church" cannot be deceived in spite of Paul’s warning in Acts 20:29-31 that the wolves would arise from among the flock. And so they have - beginning before Paul even finally closed his eyes.
Before classifying any group as a cult, Christians need to pause a moment and read the definition of the word (from a theological standpoint). All Emphasis Added
The term 'cult of Christianity' is used of a group, church or organization whose central teachings and/or practices are claimed to be biblical or representative of biblical Christianity, but which are in fact unbiblical and not Christian in nature. 
A cult of Christianity is a group of people, which claiming to be Christian, embraces a particular doctrine system taught by an individual leader, group of leaders, or organization, which (system) denies (either explicitly or implicitly) one or more of the central doctrines of the Christian Faith as taught in the sixty-six books of the Bible. 
In other words, when trying to decide on the legitimacy of a particular group that claims to be Christian, it is crucially important is that we judge by the right standard, i.e. the Bible, not tradition, creeds or so-called orthodoxy. Thus the object of this article is not to prove whether Seventh Day Adventism is or isn't a cult, but that fundamental SDA doctrine does not conform to what the Bible teaches.
Incidentally, bearing the above definitions in mind, it is a tragic fact that most of the modern church can be classified as a 'cult' because two thirds of the teachings (even in so-called orthodox churches) stem from sources other than the Bible. What is considered 'mainstream' Christianity has gone so far off the rails that it explicitly or implicitly contradicts many of the teachings of the sixty-six books of the Bible. See Footnote on Deception in The Church
Index To Chapters
Note: All emphasis in the quotes from Ellen G. White Writings (both the underlining and the occasional bolded text), has been added. Also, unless otherwise stated, Biblical quotes are from the NASB with all emphasis added)
History and Beliefs
Mission and distinguishing doctrines. The prophetic ministry of Ellen White. Origin of the Seventh Day Adventist Church - William Miller and the second advent of Christ.
Investigative Judgment - Shut Door
Investigative Judgment, Part 1: A 'spiritual" fulfillment of Daniel's prophecy? Four questions.
Investigative Judgment, Part 2: The cleansing of the Old Testament Temple. What was the Sanctuary defiled by? Daniel's vision in 8:13-14 - Context, context, context. Cleansing the Heavenly Sanctuary. The overshadowing theme of Hebrews. When is the Atonement finally complete or, to put it another way, when are we finally saved?
The Doctrine of The Shut Door: The metamorphosis of the Shut Door Doctrine. Ellen White's shut door visions. An extremely tenuous defense. So when does the door actually shut?
Ellen White True Prophet of God? Life, career and position in the SDA Church. Biblical tests for a genuine prophet of God do not include dreams and visions or fulfilled predictions. Ellen White's false prophecies.
Ellen White Vs. The Bible: Out of context and partially quoted verses, contradictions and additions to the word of God.
Ellen White's Health Reform: Biblical dietary restrictions. Ellen White's health reform included some very embarrassing statements
Ellen White's Other Teachings: Phrenology, photography, furnishings, jewelry, labour unions etc. Vitriolic criticism of Others. Preposterous opinion on leisure activities including various sports, chess and checkers, singing, concerts and reading. Examples of plagiarism.
Ellen White's Visions: Had little or no importance in the general scheme of things. Much to the contrary, they ranged from the childish and farfetched to the petty and inconsequential. Many simply served to bolster the Adventist message. The source of Ellen White's visions and her 'guides'. Advice from a dead husband.
The Sabbath and Clear Word Bible
The Sabbath: Will those who do not keep the Sabbath eventually receive the 'mark of the beast'?
The Clear Word Bible: Widely used within the Seventh-day Adventist churches, the CWB is a paraphrase that includes the teachings of Ellen White, with many words and phrases altered to reflect those teachings
 Greg Koukl. What’s the Difference Between Bad Theology and Heresy?
 Apologetics Index. Cult of Christianity. http://www.apologeticsindex.org/2765-cult-of-christianity
 Alan W. Gomes. Unmasking the Cults Paperback – Zondervan Guide to Cults and Religious Movements. Zondervan (May 11, 1995)
Footnote - Deception in The Church
The word 'deceive' means to cause someone to believe what is not true, regardless of whether the person doing the misleading is himself deluded.
One of the four most dangerous mistakes any Christian can make is to believe that they themselves, their denomination/pastor /spiritual leader, cannot be fooled. If false teachings were easy to spot, it is hardly likely that the Scriptures would warn against deception so very many times.
The 23rd chapter of the book of Jeremiah points out how widespread and treacherous deception can be. He spoke of the false shepherds that were destroying and scattering the sheep, and the "polluted" prophets and priests who spoke visions that came not from the mouth of the Lord, but from their own imaginations, thus leading the people into "futility".
The vast majority of the New Testament books have explicit and often forceful warnings about false teachers. In fact, the warnings against being deceived is a major themes in the New Testament with the words deceit, deceitful, deceitfully, deceitfulness, and deceive, used over and over again.
Paul said that "some" will fall away from the faith. However Jesus was far more explicit. He not only said that many would be led astray and few would find the narrow road, but that even the 'very elect' could be deceived.
Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it. But small is the gate and narrow the road that leads to life, and only a few find it. (Matthew 7:13-14).
For false Christs and false prophets will arise and will show great signs and wonders, so as to mislead, if possible, even the elect. (Matthew 24:24 NASB)
Both Peter and Paul very emphatically stated that wolves would arise from the flock itself
"I know that after my departure savage wolves will come in among you, not sparing the flock; and from among your own selves men will arise, speaking perverse things, to draw away the disciples after them. Therefore be on the alert, remembering that night and day for a period of three years I did not cease to admonish each one with tears. (Acts 20:29-31 NASB)
But false prophets also arose among the people, just as there will also be false teachers among you, who will secretly introduce destructive heresies, even denying the Master who bought them, bringing swift destruction upon themselves. (2 Peter 2:1 NASB)
Yet, most theologians, Bible scholars, pastors, etc. sincerely believe they themselves or their denomination, are the sole reliable interpreters of Biblical truths, and will defend to the death their version of what the Bible says. For example, although most people cannot wrap their heads around, much less explain the concept of the trinity, the vast majority of Christians believe it to be an unassailable and inviolable doctrine that comes straight from the pages of Scripture itself. In fact, numerous churches claim that one cannot be saved or called a Christian without believing in the Trinity. But is either claim true?
Read the origins of the trinity for yourself. See part five of THIS article, although reading all the chapters is even more enlightening. Note: Challenging the doctrine of the trinity does not mean challenging the Divinity of Christ and it does not mean challenging the Divinity of the Holy Spirit.
If we are smart, we had better not hang our hats on the peg labeled 'official church doctrine', on what supposedly orthodox Christians/churches think, believe, or teach, nor on what the so called early "church fathers" wrote. And we certainly had better not completely depend on what the learned scholars tell us, however highly respected and/or well known they might be. The question we need to ask is what the Bible teaches, because the only standard by which we can judge the doctrine, beliefs, and traditions of any and all who name the name of Christ is the Bible.
Unfortunately, even if the numerous warning against deception are brought to their notice or they are already aware of them, most of the Christian world is quite convinced that these cautions cannot possibly apply to them. Every Christian seems to wholeheartedly believes that the path they are on is the right one, the beliefs they hold are Biblical, and the practices they indulge in are supported by Scripture.
Christians often play a deadly game of follow the leader, often refusing to accept that well-known and well-respected leaders/preachers/authors can possibly be wrong. All too many are influenced by a charismatic preacher using out of context verses to 'prove' his or her point, others by someone claiming to have heard directly from the Lord.
And, once having decided what to believe, they hang on to it with a deadly grip. However, as the author of Proverbs said.. "There is a way which seems right to a man, But its end is the way of death". (Proverbs 14:12 NASB). See
Why Christians are Deceived.
The Four Most Dangerous Mistakes Any Christian Can Make
Fraternizing With The Enemy