If the prophet does know, my good sir, then he has lied to us all. So have any other men and women supposedly of God. How many times have opinions announced as doctrines changed? How many times did Hinckley and others say "I don't know that we teach that," or full out claim we didn't believe in something we did?
Opinions taught in an authoritative tone have changed. Doctrinal explanations taught in an authoritative tone have changed. True doctrines and practices, taught through the authority of the Holy Ghost, have also been changed or modified (Jesus Christ himself presided over the end of the ritual life of Israel and the Law of Moses, subsumed as they were in the New and Everlasting Covenant). What never changes are the principles. Core doctrines of the Church have never changed (although they have been added to and hence, expanded and amplified). Latter Day Saints believe in the same principles and doctrines they, as a people, have always believed in, even though they do not practice or apply all of them at the present time. We need not, of course, still believe in theological speculations or explanations that were never official doctrine in the first instance.
General authorities have had differing opinions of course, but they are always unanimous on the core, settled doctrines and practices of the Gospel.
And why is asking for clarification on doctrines wrong? Why is asking for a simple answer to so many questions wrong?
Who on earth is saying it is?
The face of sin today often wears the mask of tolerance.
- Thomas S. Monson