As an ex-Mormon, I had to personally confront this issue. My family, extended family, friends, neighbors, and the large majority of my hometown are Mormon, so the social costs of leaving my church were extremely high. While in high school, I was primarily in the closet, but I'd express the occasional doubt. Just the suggestion that the church could be tested against evidence resulted in people avoiding conversation with me, my now-wife being warned by mutual friends not to date me, and my parents sternly lecturing me. Note this was merely because I considered the possibility of contrary evidence, not a public expression of disbelief.
In the counterfactual world where I chose not to explore the veracity of religion, my high school years would have been significantly happier, I would have avoided prolonged conflict with my family, I would have served a two-year religious mission, and I would likely be attending BYU right now. In some ways, it does genuinely feel like this would have been better, but I can say with confidence that I made the right choice.
I could easily pick out reasons why someone shouldn't remain Mormon specifically, but I want to engage the least convenient world for why we shouldn't knowingly believe something false. Being a theist might not affect the quality of someone's everyday life much, so there is not an apparent gain from a belief in the truth. But similarly, beliefs about the moon landing, Santa, evolution, heliocentricism, etc rarely influence someone's everyday life. The problem is that once you allow exceptions to seeking evidence, allowing your beliefs to be influenced by evidence, and not starting with a bottom line, the exceptions start bleeding over into beliefs that do affect success. I don't think this slippery slope is inevitable, but if you want to win, you can't trust partitions*.
I absolutely agree that if Wednesday came to our community interested and enthusiastic, we should welcome her with open arms. Nevertheless, I would encourage her to break down any mental partitions she might have, otherwise simply note that theism is not up for discussion in the context of this site.
* This is particularly true of Mormon culture where "I prayed about it, and felt the Spirit tell me it is right" can trump any other argument.
Note this was merely because I considered the possibility of contrary evidence, not a public expression of disbelief.
Not to be a total jerk and imply you are a total jerk, but the way you merely consider the possibility of contrary evidence matters a lot. I simply want to point out that there is no chance in the world of accurately describing what you or someone like Wednesday would go through in a sentence and there is always an easy option to tilt the histories in your favor. Someone's perceptions of their own attitudes is difficult enough without t...
(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.