First of all, the protagonist John Proctor seems to be religious, in view of the fact that when he is taken to jail he does not defend himself at all; he simply accepts that he did something wrong and he can live with that. This makes him religious, because he does not want to harm the Ten Commandments. He writes a confession that he has seen the devil and that he was the only one. He even signs this paper, but as soon as Deputy Governor Danforth asks Proctor to give the confession to him, Elizabeths husband refuses and tears it up. On the one hand he does that, because he thinks that his name cannot be taken away from him; on the other hand he knows that the paper does not tell the truth. He rather wants to be hanged than to live with the thought that he has lied to the church. This is a very strong and self-confident consideration.
Another proof that John Proctor is fair can be seen in his former affair with Abigail Williams, the servant to the Perris-household. She was once in love with him, but they broke up because Proctor realized that he really could not afford to be in love with a girl while being married and having children; this makes him being fair to his wife as he does not want to hurt her. Later when Abigail threatened to tell Elizabeth about their affair he wisely chose to tell the truth to his wife. He refused not to tell her earlier, because he did not want to hurt her. It is discovered in the last act that their relationship is so strong that she forgives him. Telling her about his affair so late is probably not the best solution, but it is certainly better than saying nothing, so that Elizabeth finds our on her own.
A further indication that John Proctor is fair would be that he remains strictly faithful to his wife once he realized that having affairs while being in love with someone else is a bad conception. So when Abigail later comes to Proctor to ask him for continuing their relationship the protagonist refuses. He cannot do this to himself or to his wife. Otherwise he would commit adultery once more. Again, this makes him being fair to his wife.
In conclusion one can say that the character John Proctor is a quite fair person. After he realizes some thingsfor example, having an affair is not the best while being marriedhe tries to do the best for himself and the people around him. This includes no voluntarily contact with Abigail. They only talk when he tells her that he cannot or does not want her anymore. Finally he pays with his life for committing adultery. This action is one of the most expressive acts in the whole play. John Proctor is a good and noble man and because of this he believes that he cant be hanged and die a martyr when he has this sin blooming over him every waking moment.