At What Point is it Too Much?

I saw a special last night on PBS about Jim Jones and the People's Temple (watch it here). It really got me thinking; I wonder at what point his followers would have said it was too much. I wonder why so many of them waited until the last second to flee, and why even more (over 900) stayed with him to the very end and drank the punch that they knew would end their lives.

Certainly, these people had clues earlier that something was not right. Jones humiliated them publicly, guilted them into working for days without sleep, even coerced some of the men and women to have sex with him. Yet hundreds followed him to their deaths. What is it that keeps people blind to the obvious clues about a man's true character? They see in him only what they want to see. They overlook his obvious character flaws and horrible acts and deny their discomfort. At what point would Jones' followers all have said, "This is just too much. I cannot follow you any further"? The sad truth is that more than 900 never reached that point. Men and women murdered for him in cold blood and many killed their own children because he said to.
Long before the congressman came to visit, Jones asked his followers to drink some punch. After they had all drunk, he told them they had just drunk poison. After seeing their reactions, he told them that it was merely a test; they hadn't actually drunk poison, but he wanted to test their loyalty.

It was suggested on the special that it wasn't at all a test of loyalty; Jones knew they were loyal. They came every day, worked hard every day, turned in their paychecks every week, etc. Jones had no reason to question their loyalty. That test was not for them, but it was for Jones. He wanted to see if he had absolute power over these people. And he got his answer.

I couldn't help but be reminded of a few incidents in Joseph Smith's life. In order to "test" some of his followers (e.g., John Taylor and Heber C. Kimball), he informed them that he had been commanded to marry their wives. After some anguishing soul-searching, they gave him their submission. Only after they relented did Smith tell them it was only a test of their loyalty.
Or perhaps it was Smith's test to make sure he did have absolute power over these men.

And so, at what point would some no longer believe Smith was a prophet? How far is he allowed to go?

References
Kimball, S. J. (1986). Heber C. Kimball: Mormon patriarch and pioneer. Champaigne, IL: University of Illinois Press.

Prophet Wilford Woodruff, John Mills Whitaker Journal, Nov. 1 1890