In The Crucible, what message is Arthur Miller trying to get across to the reader?

I think that the author's main message in this play is
that people should be aware of how much we can get swept up in hysteria and what bad
things can occur when we do.  He is saying that we tend to lose our heads when we are
afraid of something.

In the play, the people of Salem lose
their heads because they are afraid for various reasons (that Miller explains in the
notes).  Because they are afraid, they fall for the silly stories made up by Abby and
her friends.

Miller is warning us that we tend to persecute
people when we are afraid.  Hysteria hits us and we forget our better natures and turn
on a convenient scapegoat.