(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.
Stephanie Meyer's "Twilight" books are fascinating in this regard. Meyer is Mormon and she doesn't inject her religion into her books any obvious ways (for example, theological issues are never mentioned and none of the characters attends church) but there is a fascinating "pro life" theme that includes both the desire to procreate and the desire to be an immortal vampire if and only if it is possible to be a vampire who restrains their innate urge to tear out the necks of mortals and feast upon their blood.
Once I started reading vampire chick lit with an interpretative frame that it was a sort of "publicly accessible" meditation on the real world ethics of transhumanist immortalism, these stories became a lot more philosophically interesting. I watched Vampire Hunter D after seeing the connection and found myself rooting for the vampire :-P
The critical thing I'm trying to point to is that Meyer's story appears to be anti-abortion and also pro-vampire. And then there's the existence of the Mormon Transhumanist Association...
Personally I think that the lesswrong community might have a phobic reaction to theism specifically because some religious people (especially first generation converts to new religions of which Mormonism has many) are prone to mentally flinching from obvious conclusions... and sometimes they use their theology to justify doing kind of messed up things to their children. The children grow up and sometimes leap to specifically materialist atheism in an emotional counter-reaction.
I have not seen strong evidence in either direction for materialism versus an idea like simulationism except to the degree that materialism inherently pre-judges the answers to questions like (1) whether there might be some "supernatural" monkey business going on in the corners of apparent physical reality or (2) whether a timing attack on physics might produce interesting results (or cause reality to crash).
I think second and third generation theists are more likely to be open to the idea of cryonics and the reasonableness of ethically pursued transhumanist aspirations. You can put all kinds of mumbo-jumbo in people's heads, and while it might make them very frustrating parents, after a generation or three I don't think it will hurt very much, and it might selfishly help them cooperate with other members of their tribe (more than it hurts government policy if people signal their tribal allegiance by voting for, say, dumb educational policies).
By the same token, it wouldn't totally surprise me if first generation converts from theism to rationality may be going beyond the evidence in some of their initial conclusions, specifically because of the passion with which they left a fundamentalist theism and started subscribing to "fundamentalist rationality".
I don't see a sufficient justification to interpret Twilight as anti-abortion independent of the fact that Meyer is a Mormon. It's against forced abortion, but the person whose choice is relevant - the pregnant woman - wants her baby, and takes steps to keep it, over the objections of generally sympathetic characters who advise her otherwise.