Similar things happen in religion. Those demanding quick and easy answers - easy comfort - can readily find reasons why Joseph Smith was not a prophet. He taught Disagreeable Doctrine X or promoted Objectionable Practice Y or made Silly Mistake Z, and therefore he is a fraud.
But truth is more complicated than that.
Joseph was either a prophet of not - yes, I think that's a fair statement. But then how do we evaluate it? Some take the following approach:
1. A true prophet must have divine power from God.This approach, of course, is based on faulty assumptions. The search for truth requires careful consideration of assumptions, of alternatives, of frames of reference. A simple "slam dunk" argument with seemingly straightforward logic is not all that is needed, especially when it's based on errant assumptions.
2. Divine power makes you omniscient, infallible, invincible, and able to leap tall buildings in a single bound.
3. Joseph Smith did not know everything, made some mistakes, was easily killed by ordinary bullets, and had an absolutely dismal track record when it came to leaping and buildings. (His only recorded attempt involved falling from the window of the Carthage Jail - and it was falling down only, after which he was dead. Not very impressive.)
4. Therefore, Joseph Smith was not a true prophet. Q.E.D.
The real issue is not what kind of mistakes Joseph did or did not make or how many documents and witnesses weight in his favor or not. The real issue is whether he was called of God. Did He see God? Did angels minister to him? Was he given gold plates to translate by the power of God? These are the real issues, and the best way to assess them, in my opinion, is through an examination of the Book of Mormon. If it is divine, then we've got a prophet on our hands, regardless of how thick any anti-Mormon book is.
For those seeking understanding or even truth, it's not enough to flag an apparent contradiction or discrepancy. One must dig and ask further questions. Could there be another explanation? Could something else be understood or meant? Are my assumptions correct? Is the issue really relevant? Consider the Biblical account of the Creation. It says the earth was created in six days. Scientific evidence suggest that billions of years were involved in the development of the earth and its life forms. For many, this clash is enough to justify atheism or at least a rejection of the Bible. But for those seeking truth, a less comfortable process is needed. One must do a little work and ask further questions. Does the word "day" in the Bible really mean a 24-hour period, or could it accommodate much longer periods of time? Is the Genesis account meant to provide revealed scientific details about the Creation, or meant to simply affirm that God was the Creator and did His work in stages? If the revelations in Genesis are incomplete, imperfect, or have been altered by men without scientific knowledge, does that mandate rejection of the rest of the scriptural record? Are there aspects of Genesis that do accord with scientific understanding? How important should the scientific implications of Genesis be?
This process of examining assumptions and continually seeking for truth is also a healthy one for people of faith, including LDS folks. The task of reconciling all knowledge into one great whole is actually consistent with the teachings of the Gospel. It may require discarding some of our own assumptions - like the errant assumption that the Book of Mormon describes ALL migrations to the New World, or encompasses all of North and South America. Critics are wildly uncomfortable that we can adjust our understanding of the text or of other LDS issues based on further information obtained by science or even by revelation. They are more comfortable locking us into the nineteenth century, where it is easy to find puzzling unofficial quotes and teachings from various sources that can be caricatured - things we don't accept and need not defend. When we say that we don't share such views or don't believe such teachings, they treat it as a scandal - as if religious understanding could not develop and grow over time.
True scientific knowledge and true religious knowledge demand flexibility from the thinker - the ability to overcome limitations in understanding and to revise paradigms and theories. Yes, this leads to the terror of uncertainty, the discomfort of work, and the tension between the known and the unknown, but there are few easy answers when dealing with the biggest issues of all. There are some things that we can establish with certainty through spiritual and sometimes intellectual means: the existence of Jesus Christ, the divine power in the restored Gospel, the reality of the Book of Mormon, but that doesn't settle every issue or answer every mystery, anymore than knowledge of the great Laws of Thermodynamics lets us explain the nature of time, gravity, and quarks.
For those seeking truth, there are answers, but they won't always be found in a library or even via Google. If there is a loving God - and there is! - ultimately we must turn to Him as we do the best we can with our minds to determine what is real and what really matters. We can appeal for Him to know if Jesus Christ is the Savior. Through a combination of study, pondering, mental exploration, and sincere prayer, we can also know that the Book of Mormon is an authentic ancient record that is also a testament of Jesus Christ, another witness with the Bible for the true Messiah. Neither book is perfect, and both can be dismissed by those looking for the comfort of "easy" arguments against them (the Book of Mormon contains a modern French word, for heaven's sake - what a fraud! - and it even contains hundreds of English words!). But for those willing to do the work of seeking for truth, a rich and intellectually rewarding journey awaits you.
Joseph Smith was a prophet of God - and the Book of Mormon provides massive, documented evidence to support that claim. We don't need to argue over various ways to interpret minor prophecies in the Doctrine and Covenants. He gave us 500 pages of an ancient text to hang himself with, filled with details and place names like Nahom that leave no room for treating it as warm and fuzzy fiction. It's an ancient text or not, a text inspired of God or not. I urge you to examine it carefully and sincerely - give it every test you can, and seek the help of our loving Heavenly Father in honestly seeking for truth. Then you, too, can know for yourself.