This comment, from another post, is typical of what I have heard from other people:
In 1839, Joseph Smith was asked to describe the difference between his religion and the other religions of his day. Smith replied that the primary difference was primarily in mode of baptism and the gift of the Holy Ghost by the laying on of hands (HC 4:42). However, Smith neglected to mention that he believed that his visions were contrary to classical Christianity. He needed to tell them that, “God the Father and His son Jesus Christ, appeared to Joseph Smith in the spring of 1820. Joseph revealed that the Father and the Son each have a body of flesh and bones as tangible as man’s,” (D&C 130:22). Smith’s answer is obviously evasive. He neglected to explain his view of God as in the form of a man, the importance of works, temple ordinances, polygamy and deification.
Another way this same basic question has been phrased in the form of a statement is “Mormon missionaries only teach the stuff that appeals to mainstream Christians and then once they’re baptized they throw all the stuff at them like baptism for the dead and man > God doctrine after it’s too late.”
There are at least two reasons why Joseph Smith didn’t mention these other things in the situation above, and why Mormon missionaries don’t teach certain things.
One reason is because there is limited time and space. Joseph Smith was being asked by a newspaper reporter what the “primary” difference was between the LDS Church and other religions. Surely the questioner didn’t have time for and wasn’t looking for Joseph to sit down and take 30 hours to answer him. Even if Joseph spoke for 30 hours straight there are still things he wouldn’t be able to cover and people could still say “See? He’s being evasive!” Just because something isn’t mentioned doesn’t mean it’s being hidden. When people ask me how I’m doing I generally just say “Good” rather than giving them a five-minute explanation of all the good things going on in my life.
A second reason for stating certain things first and other things later is for the same reason certain things are taught to elementary school children and other things are taught to high-school aged kids. You could hardly say that school administrators are sneaky in how they teach kids basic math in elementary school but then throw calculus at them in high school when it’s “too late”. Although I will admit that I did feel a bit betrayed by my upper math classes. There is a progression of ideas in the gospel as with anything else, and it only makes sense to start by teaching those things that are more basic and fundamental, which of course includes those things that are generally understood by the majority of the population.
But aside from this, it’s simply not true that all Mormon missionaries teach is non-controversial ideas that are easy to accept. Traditionally, Mormon missionaries teach about Joseph Smith and the Book of Mormon in the very first meeting with someone who wants to learn more about the LDS Church. If modern-day prophets, Joseph Smith saying that he saw God and Christ appear to him as two distinct being, and scriptures in addition to the Bible aren’t shocking enough for a first introduction to the LDS Church then what is?
Mormon missionaries simply can’t teach it all, and there’s a logical order in which to teach things. Nothing is hidden from those who want to learn about the church, and frequently things like temple garments, baptism for the dead, man > God, and other things are discussed between missionaries and investigators of the church. To me, it seems that no matter what missionaries teach the enemies of the church are going to try and find fault with it, and saying that Mormons are hiding things is an easy target, since there’s so much Mormons couldn’t possibly cover even if they tried.
By the way, in case you’re interested, the LDS Church publishes the entire missionary manual online for anybody to read. If you want to know what Mormon missionaries teach and how they’re taught to teach it, you can read the book and find out for yourself.