The original question was "How can a person have a strong testimony and then turn their back on it?"
This question presents a conundrum for this site. It would be best answered by someone who has experienced the question asked. Yet most, myself included, would be reticent to share their feelings for several reasons. One of those could be that their knowledge or reasons stated could be viewed as anti mormon, even if this were not at all the intention.
I am not referring to most of the situations being discussed in this thread as I have seen too many people use the excuse that they were offended. And while yes people can be offensive, especially in our Church, we should be in the Church because we believe the teachings are true above all else. Also I know that people can become inactive and still live most if not all of the Gospel principles with the exception of attanding Church every Sunday.
But, what if I start to question one of the Churches teachings. I will not go any further than this as it is not my desire in the least to be the cause of anyone to question the Church. But I do wish I could discuss it so as to resolve my feelings.
But what if after much reading, research, and study, I cannot truly answer that I believe every single thing that the Church teaches. Does that make me no longer a mormon. Does that mean "I have lost my testimony" even though I believe in all the principles and precepts of the Gospel.
If I "come clean" with my leaders, I may risk losing temple recommend, priesthood, membership. And to be quite honest, I want my family to stay active. I want to stay active. I want to see the rest of my children married in the Temple. Let me make this clear, I am not refering to any sinful action or deed on my part whatsoever. I am in an untenable position as I can't state my issue, and as I reread my own explanation I realize I am not making much sense.
How about if I use an actual event to descibe a hypothetical that is a close analogy. The Mountain Meadows massacre, what if one were to believe that a prophet did direct that action, and I am not saying I do or that one did, but what if. And what if this action was claimed to be prophetic (it wasn't and I am not implying it was, this is just a hypothetical) and one could just not believe that a prophet would do that. Similar in that some people have a hard time in the thought that Nephi was commanded by God to kill in order to obtian the plates. My personal belief struggle is on a similar plane.
So perhaps this question would be best asked with more specifics attached. One can have a testimony about many things, and therefore lose, or possibly never have a testinony about many subjects.