(I only skimmed all the previous posts, so sorry if was brought up already)
As someone who grew up in Utah, my mom is from a very small town in Wyoming, and in the morning culture in the 90s. I totally see how this happened.
The Mormon community is a very unique one. Kind of how someone brought up people willing to sacrifice their children to cults and cult leaders.
This guy was a wonderful manipulator. And played the parents perfectly to get what he needed from them. That girl didn't stand a chance, nor did her parents.
It's really hard for anyone who hasn't been submeresed in the Mormon culture to understand. They are very trusting, naive, ignorant to bad things/people. I mean, there were (as with several different religions) Bishops regularly molesting, raping young girls when they had their private meetings. And nothing was ever said or done about it, and that came out in the last 10 or so years. Let alone almost 50 years ago!
Is it horrific and crazy, yes. But unreasonable and unrealistic? Not in the least.