Reverend Hale is sincere and naive. I do believe that his is a man of strong moral conviction, but I think that part of his character is that he has too much faith in man's ability to do good, which is what makes him naive. He believes that witches and demons are real and has honest means of trying to discover if they are truly the cause of the girls affliction. The fact that he has investigated witchcraft before, and admitted to not finding witches in previous towns, shows that he is sincere in his methods. The problem is that he assumes that Parris and the girls are being truthful, and that they are honest in their presentation. He also assumes that they are telling him all the information that he needs to know. He trusts the wrong people, believing that Parris as a Pastor is incapable of being dishonest or deceptive.
We see that the end of the play that Hale's viewpoint has changed, and he is not afraid to admit that he was wrong or that the girls are frauds. He sets out to save the lives of the innocent at any cost, feeling personally responsible for allowing things to progress as far as they did. His remorse and fervency reinforces his sincerity and conviction.