I don't know what, if any, official stance is and haven't read through the rest of the thread yet, so I can only give my opinion here. I'm one of those people who reads everything. When I was first meeting with the missionaries before joining the church, I often read other stuff, some of it downright anti-Mormon. They never discouraged it, and it often led to some really good questions I never would have thought up on my own. My personal theory is that truth is truth, no matter what else you read. It may lead to questions, maybe even doubts, but if you approach it with openness and prayer, ultimately the truth will win out, and leave you with a much stronger faith when it does. As for what the missionaries are allowed to read, I can understand restrictions there. They have a job to do and need to stay focused.