By this point in the story it is obvious to Rev. Hale, and I believe to Parris, that these people are moral, they are telling the truth that they are not witches, and that they will go down as martyrs, not villians if hung at this point.
The reading audience knows the truth, it appears that the townspeople are able to see through the girls and their spectral evidence. The only ones still hanging on the to lies as if they are truth are the magistrates.
This play so interestingly demonstrates man's awareness of his own sin. John knew his, wrestled with God about it, and received forgiveness. Parris, a holy man, wanted to hide the truth from his flock and got worked up about money and church attendance. Repentant heart for these things? No, not really. So, you get the chance to determine the measure of a man in this piece. I think that is part of what Parris is realizing in these simple words. Proctor's life was worth preserving, he had much to teach his sons and was ready to live a righteous life, but admit mistakes.