While we may disagree regarding some topics, I am interested to hear what the most influential factor was that led you to leave the church.
I'm not interested in changing your belief system or world view or arguing doctrines, I just want to respectfully hear the points of view of anybody willing to share them.
Hiram, your post makes me very happy. I rejoice whenever I see a person earnestly inviting others to share things that currently go against what that person believes. It is a hallmark of maturity and wisdom when we invite those kind of dialogues, for that is how we set the stage to learn. We listen and consider. It doesn't mean that we will necessarily give up our beliefs, but we will be better for at least having considered and weighed another's point of view. We might even find that we did not know as much as we thought we knew and in light of the new info must change our thinking on the matter. I once wrote a post on the critical necessity of reading articles critical of your current beliefs - it is as important for non-believing postMormons as it is for TBM's. I invite you to not make this post a one time thing, but continue to seek out opposing view.
Now, on to your question. Occasionally, polls are conducted on the forum to ascertain what the final straw was for each of us. Here is a link to one such poll. As you will notice, the Book of Abraham topped the list, followed by the Book of Mormon. The Book of Abraham was my personal coup de grace as well. First, let me tell you a little about myself. I once was an uber-TBM. I went to BYU, taught at the MTC for almost 3 years, was 2nd Counselor in two Bishoprics, and was an amateur apologist for the church resolving people's concerns with Mormonism both online and in person. Members looked up to me as someone very knowledgeable in the gospel and very spiritual. I knew most of the issues that can concern Mormons about their history and the standard apologetic responses, from Joseph's peep stone money digging to polyandry and Joseph's marrying his own teenage foster daughters to Masonic origins of temple signs and tokens, etc.
The apologist actually has an easy job. His is not to prove the Church is true. All he needs to do is demonstrate that the critics' evidence is not sufficient to prove the Church is not true - that there is some possibility that the Church might be true despite all of this challenging evidence. If the possibility remains, then it falls on each individual to exercise faith in that possibility that the Church is true and receive a witness of the Spirit that it is true, etc. The apologist is not concerned with what is most likely to be true (probable), only with maintaining that the Church might still be true (possible). That approach works very well in maintaining one's faith. One can find all sorts of ways to twist and adjust one's understanding of what it means to be a prophet to make it work. We PostMormons call that mental gymnastics.
Then, I had a friend whose mother left the Church and had supposedly become "anti". That friend wanted to save her and show her the error of her ways. He began studying what she had read so that he could counter her arguments, but he ended up being convinced himself that the Church wasn't true. Well, as an amateur apologist, I felt that I had been around the block a few times because "I had heard it all before". I thought I might be able to show him why whatever he had read did not prove the Church wasn't true. We discussed many issues from Blood Atonement to Adam-God doctrine to Danites to Masons, etc. But, then we got to the Book of Abraham. Now, I thought I knew all about the Book of Abraham issues, that it wasn't an actual translation of the rediscovered papyri, etc. But, my friend did bring up some things I had not heard of before, like the penciled in drawing of a priest in facsimile #1 where Anubis was supposed to be. I didn't really understand the significance at the time, I let it go and "shelved the issue" as we say around here. I never made any progress with reconverting my friend and figured he was just hopelessly lost, having no faith.
Anyway, two years later, something someone said on one of the apologist websites renewed the issue of the Book of Abraham in my mind. This time I determined I would get to the bottom of it so that next time I came across someone with Book of Abraham concerns I could intelligently resolve them. This launched a six month long investigation. I read everything critical, apologetic, and original sources. I took no one's word for anything. If I read an article in which the author claimed anachronisms, I read books on Egyptology until I knew for myself that yes, the land of Egypt got its name from the Greeks, not from the character Egyptus as the Book of Abraham claims. I read the Kirtland Egyptian Papers, including Joseph Smith's Egyptian Alphabet and Grammar, I read Ritner's actual translation of the recovered papyri, I have seen high quality copies of the papyri, read the writings of Hugh Nibley, Jeff Lindsey, Kerry Shirts, John Gee, Daniel Petersen, etc, John Larsen, Kevin Mathie, John Day, etc, I have learned a lot about the ancient Egyptian religion, including Breathing Permits, Anubis, Osiris, Book of the Dead, etc. My knowledge of this Book of Abraham issue approaches that of an expert.
I began with the eye of an apologist, looking for any interpretation I could find that would still leave the possibility open that Joseph was still a prophet, seer, revelator, and translator. I, of course, encountered numerous apologetic explanations, but I eventually had to reject them all, for they were unworkable, the evidence simply left no room for them. They only work if you are either ignorant of or ignore parts of the evidence. There is no hole for the apologist to exploit. The case against the Book of Abraham is air tight and bullet proof. There is no uncertainty for faith to work in; no doubt to give the benefit of. If one wants absolute proof of fraud within Mormonism, one need look no further than the Book of Abraham. I think that is one reason why it ranks so highly in the polls of what was the final blow to our faith in Mormonism.
I believed that the Spirit had told me the Book of Abraham was exactly what Joseph claimed it to be: a translation of papyri written by the hand of Abraham; and I now had evidence to prove that it was nothing of the sort. It could not even be a true revelation, despite the whole translation issue, because the text contains anachronisms and incorrect reconstructions of history. Oh, and lest you buy into that old line that the text has all these marvelous parallels to ancient traditions about the life of Abraham, I invite you to really take a look at it. Read John Gee's book and then critically evaluate it running through every reference. You see so very few apologists or TBM's put the time into this that they need to. They hear a good theory that maintains their faith, embrace it, and pass it on, without having researched it themselves. I am currently working on a paper that will be a more formal rebuttal of just this "parallels with ancient text" argument. You can read a preview here.
OK, so the "Spirit told me the BoA was true", and yet it absolutely could not be. And it was not just a personal failure to interpret the Spirit correctly, for all the latter-day prophets and apostles presumably also believe the Spirit has told them it is what Joseph claimed it to be. I mean, it was ratified as scripture as part of the Pearl of Great Price in general conference. Yet, they all were mistaken. It appears that no one can tell when the Spirit is telling them the truth or a lie. At minimum this means that the Spirit is an unreliable way to discern what is true from what is false. And now that the witness of the Spirit is suspect, what does that mean for the weight of the evidence against the church. One starts to get sick to one's stomach when they consider that Joseph's promiscuity was not sanctioned by God. He slept with girls as young as fourteen, as close in relationship as foster daughters, and he slept with other men's wives. How revolting? How disgusting? And Brigham Young's Blood Atonement and Mountain Meadows Massacre and the deeds of the Danites...how corrupt and evil? And the discrimination against blacks, and gays, and the subjugation of women...ohhh*puke*. Mormonism begins to look no different from any other cult.
Well, what about the good that is done and answered prayers and such? Doesn't that prove the Church is true? I have found that there is nothing that requires us to reject natural explanations for those things in favor of supernatural explanations. We could talk about this for hours. But, if you want to understand why I no longer believe in Mormonism, begin by investigating why the apologist explanations for the Book of Abraham don't work and why there is no room for any explanation to work that doesn't result in acknowledging that the Book of Abraham isn't what Joseph claimed it to be.