Answer:
Because he acknowledges his mistakes and repents of his failures
Step-by-step explanation:
Although John Proctor's morality is questionable because of his adulterous and disrespectful behavior, in the course of the book he shows traces of morality when he feels guilty for everything he has done and seeks to repair the damage he has caused as a way of being redeemed from his sins.
As he acknowledges and seeks forgiveness for his failures he can be considered a moral and ethical person.