(Disclaimer: This post is sympathetic to a certain subset of theists. I am not myself a theist, nor have I ever been one. I do not intend to justify all varieties of theism, nor do I intend to justify much in the way of common theistic behavior.)
I'm not adopted. You all believe me, right? How do you think I came by this information, that you're confident in my statement? The obvious and correct answer is that my parents told me so1. Why do I believe them? Well, they would be in a position to know the answer, and they have been generally honest and sincere in their statements to me. A false belief on the subject could be hazardous to me, if I report inaccurate family history to physicians, and I believe that my parents have my safety in mind. I know of the existence of adopted people; the possibility isn't completely absent from my mind - but I believe quite confidently that I am not among those people, because my parents say otherwise.
Now let's consider another example. I have a friend who plans to name her first daughter Wednesday. Wednesday will also not be adopted, but that isn't the part of the example that is important: Wednesday will grow up in Provo, Utah, in a Mormon family in a Mormon community with Mormon friends, classmates, and neighbors, attending an LDS church every week and reading scripture and participating in church activities. It is overwhelmingly likely that she will believe the doctrines of the LDS church, because not only her parents, but virtually everyone she knows will reinforce these beliefs in her. Given the particular nuances of Mormonism as opposed to other forms of Christianity, Wednesday will also be regularly informed that several of these people are in a position to have special knowledge on the subject via direct prayer-derived evidence2 - in much the same way that her parents will have special knowledge of her non-adopted status via direct experience when she wasn't in a state suitable to notice or remember the events. Also, a false belief on the subject could have all kinds of bad consequences - if the Muslims are right, for instance, no doubt Hell awaits Wednesday and her family - so if she also correctly assumes that her parents have her best interests at heart, she'll assume they would do their best to give her accurate information.
Atheism tends to be treated as an open-and-shut case here and in other intellectually sophisticated venues, but is that fair? What about Wednesday? What would have to happen to her to get her to give up those beliefs? Well, for starters, she'd have to dramatically change her opinion of her family. Her parents care enough about honesty that they are already planning not to deceive her about Santa Claus - should she believe that they're liars? They're both college-educated, clever people, who read a lot and think carefully about (some) things - should she believe that they're fools? They've traveled around the world and have friends like me who are, vocally, non-Mormons and even non-Christians - should she believe that her parents have not been exposed to other ideas?
Would giving up her religion help Wednesday win? I don't think her family would outright reject her for it, but it would definitely strain those valued relationships, and some of the aforementioned friends, classmates, and neighbors would certainly react badly. It doesn't seem that it would make her any richer, happier, more successful - especially if she carries on living in Utah3. (I reject out of hand the idea that she should deconvert in the closet and systematically lie to everyone she knows.) It would make her right. And that would be all it would do - if she were lucky.
Is it really essential that, as a community, we exclude or dismiss or reflexively criticize theists who are good at partitioning, who like and are good at rational reasoning in every other sphere - and who just have higher priorities than being right? I have priorities that I'd probably put ahead of being right, too; I'm just not in a position where I really have to choose between "keeping my friends and being right", "feeling at home and being right", "eating this week and being right". That's my luck, not my cleverness, at work.
When Wednesday has been born and has learned to read, it would be nice if there were a place for her here.
1I have other evidence - I have inherited some physical characteristics from my parents and have seen my birth certificate - but the point is that this is something I would take their word for even if I didn't take after them very strongly and had never seen the documentation.
2Mormons believe in direct revelation, and they also believe that priesthood authorities are entitled to receive revelations for those over whom they have said authority (e.g. fathers for their children, husbands for their wives, etc.).
3I have lived in Salt Lake City, and during this time was, as always, openly an atheist. Everyone was tolerant of me, but I do not think it improved my situation in any way.
I'm not really sure how much I should reply to any of this... I'm not trying to convince you that your religion is wrong. Most of my family is still Mormon, so I'm quite good at hanging out with Mormons and not trying to convince them that they are wrong. (In fact, my deeply-ingrained strategy is to avoid conversations just like the one we are having right now.)
Perhaps I should start at the end:
No, I really don't have to find them internally... I just have to find them within myself. I was not attempting to debunk Mormonism. (There are plenty of sites out there that do that, though, if you are really interested...) This was originally about Wednesday, and what I was saying (or trying to say) was that I could not live with the contradictions between what I believed and what Mormons are "supposed to" believe.
Perhaps this is all revolving around the word "contradiction"... and perhaps I should have used a different word.
And with that, I'm not sure I should even address your points. "Animals are for the benefit and use of man," for example... well, yeah, I just don't believe that. You state it like it's fact.
In general, on morality: if it doesn't hurt someone, it isn't wrong. I didn't think I needed to say that, but I haven't talked to religious people about "right and wrong" in a long, long time. I haven't met anyone who honestly thought masturbation was wrong in a long time... guess I'm out of practice. :-) Obviously "fun" is neither necessary nor sufficient for something to be "not wrong". My point: if it doesn't hurt anyone, then it isn't wrong. And if it's also fun, then Mormonism hurts you by making your life less wonderful than it could have been (at least in that instance).
As for contradictions in fact: there were no horses in America. There was no Flood, and no Adam and Eve. I know Mormons have that "as far as it is translated correctly" clause for the Bible, but even so: if a book is the word of God, it shouldn't be factually incorrect, should it? (And it shouldn't contain spelling errors.)
And you glossed right over the "there is no God" part. Well, do what you need to do, but for many of us: the absence of God is as much a fact as the existence of the Sun. So a book that says "there is a God" is contradicting the facts.
This is not a logic game to me: this is about what is really right and wrong, and how best to live in this short life we get (since it's the only one we get). And for dear Wednesday's sake, I hope she gets as much joy and beauty and excitement and fun that life has to offer!
And some of that involves alcohol (taken responsibly (which is not the same as "in moderation" in all cases)). And some of that (well, kind of a lot at some points) involves masturbation. And, if she plays her cards right, some of that might even involve polyamory or bisexuality or any of the billions of ways to love people. It's what I want for my own children, and it's what I want for Wednesday.
But in the Mormon church... I just don't think she's going to find that.