How does The Crucible teach us how power has been shifted around when challenged?

Power shifts several times in The Crucible.  First, Tituba and the girls become extremely powerful at the end of Act 1; a slave and a group of young girls are hardly the sort of people who would typically have a great deal of power in Salem in 1692: consider Parris's threat to beat both Tituba and Abigail in this act.  However, with their accusations of witchcraft, accusations that seem to confirm the worst fears of a few, power shifts away from those who typically have it to those who typically don't.  The cause?  Fear.  The accusations seem to justify the fears of people like Mrs. Putnam, and once others begin to realize the extreme power the girls now wield (as well as how they might help put this power to use for their own ends), the girls' power is cemented.

Later, in Act Three, the power typically held by a judge or the deputy governor of the colony is shifted away from them and onto the girls.  Again, fear is the major reason for the shift.  Danforth first acquires his power by instilling fear in others.  He tells Francis Nurse that "a person is either with this court or he must be counted against it, there be no road between."  His goal seems to be to make people afraid that they will be considered one of the individuals who are "against" the court; such a fear would silence them and prevent them from preventing evidence that would seem to contradict the girls' statements.  Abigail then shifts the power dynamic again when she instills fear in Danforth.  When Proctor confesses his affair with Abigail and Danforth questions her about it, she eventually says "in an open threat: Let you beware, Mr. Danforth.  Think you to be so mighty that the power of Hell may not turn your wits?  Beware of it!"  Thus, she threatens him with an accusation, making him fearful, and causing him to defer to her power moving forward.  

All of these shifts seem to teach us that fear is dangerous.  Fear strips us of our reason and our compassion, compelling us to behave in ways that we normally would not, to believe statements we would typically doubt.  John F. Kennedy once said that "We have nothing to fear but fear itself," and The Crucible seems to support such a statement.