I think that Miller sincerely believes that drama and art, in general, can help to facilitate social change. The fabric of transformational reality is something that is evident in Miller's work. I would point to the ending as a part of this. The ending of the work where Proctor reclaims his name as being the most important element of his being represents how his actions can be both inspirational to others and embodies how individuals have power and autonomy. In a context where individuals seemed powerless against the overarching and encroaching element of authority in the form of HUAC, Miller's drama reminds all of us that human freedom can be acted upon in the most dire of conditions. If human beings possess the courage, like Proctor or like Giles Corey, they can act in a manner that shows what should be as opposed to what is. In this, Miller is able to convey the idea of how individuals can "change the world." Arising from the ashes of the Holocaust and in the midst of McCarthyism, this is a very compelling message and one that can compel much in way of change and transformation. In this, I think that Miller was trying to convey much about power and individual reaction to it in the modern setting in the drama.
At the heart of this play is the message that fear of the unknown and uncontrollable breads hysteria. Fearing something because you can't see it or understand it is no reason to fear it. If enough people buy into this fear hysteria, or excessive fear, will ensue. It is in this state of hysteria that bad things happen, and bad people will take advantage of this situation. In the play people are killed out of fear of witchcraft and this quickly de-evolves into accusations being made for the benefit of the accuser. It is about the at the time of the end of the play that the powers that be in the play realize that this has gone out of control.
Sadly, this really happened in Salem and 21 people died due to hysteria and the abuse of the situation by advantageous townspeople.
Miller used this to prove his point, as mentioned about. This play also has undertones of McCarthyism, which was just a modern day witch hunt. He didn't agree that being afraid for fears sake made any sense.