Bergman cites many studies done on the subject. Please see http://www.seanet.com/~raines/mental.html . But even if you're not a Bergman fan, there have been many studies done on stress. It has been proven that people can deal with lots of stress if they are able to manage their circumstances. But there is no room for self management within the org. The WTB&TS gives its expectations, and pressure is mounted on the rank and file to follow to the letter. If you do just the minimum of 10 hours a month in field service and preparation for and attendance of all meetings, what time is left for anything else for those who work a fulltime job or are raising children?
Even for those few who don't have a time issue, what about the heart wrenching decisions that must be made in relation to blood transfusions, the required shunning of disfellowshipped loved ones, and the fact that abuse victims are shushed at best, and accused of wrongdoing at worst? Throw in the restrictions on independent thinking and recreation, and you've got the perfect cocktail for crazy. If you weren't nuts when you joined the cult, you'll wind up nuts after being in it for awhile.