John Proctor has been a voice of reason thus far in the play, because he knows that the girls are faking. Abigail told him, when Betty was sick, that the girls were only "sporting" in the woods, having fun, that no witchcraft was involved. Proctor believes that the whole thing will blow over and that nothing will come of it.
He continues to believe that it will work itself out, even after people begin getting arrested. He believes that the court will come to its senses and that the innocent will be freed. He believes in justice, in the legitimacy of the court and respects the law.
At the end of Act II, Proctor, the only one who knows the truth from Abigail's own lips, is defiant against the authority that comes to arrest his wife. He tears up the arrest warrant, refusing to accept that the whole town has gone insane. He thought that if he kept his distance from the witchcraft hysteria that his family would be safe.
Now that his wife is accused, by Abigail, and he knows why, he gets very angry. He fights, demanding that his wife not be chained. He is determined to shine the light of truth on the court the next day, he will bring Mary Warren in to testify that the girls are only pretending and that she made the poppet, and stuck the needle in the belly, for safekeeping. There is no witchcraft, he is sure they will listen and that Elizabeth will go free.