You have to keep in mind that Cast Members are no different than everyone else out in the "real world". Yes, they have a reputation among the public as constantly smiling and whistling "zip-a-dee-do-dah" all day. And having a positive, bubbly personality helps get them hired. But we can ALL turn on the charm in an interview.
But take that happy, smiling Newbie and subject them to 8 hours of rude, arrogant, inconsiderate guests and it breaks them down. Keep in mind they don't go through any sort of "Psychological Bootcamp" during training. It's all peaches and cream and welcome to the magic. What they need is a day of "torture training" to toughen them up, and prepare them for what lies ahead.
Perfect example was this afternoon. The "no camping policy" before the parade has been abandoned. There was just no way to enforce it when the guests refused to obey. Unless getting kicked out of the park for not complying becomes policy, they simply refuse. Imagine the frustration of a handful of CMs working Main Street trying to do their job and NO ONE listens to them...respects them. Would you be able to maintain a fake smile under those conditions?