12 Let the mouth too fast from disgraceful speeches and railing. For what does it profit if we abstain from birds and fishes; and yet bite and devour our brethren? The evil speaker eats the flesh of his brother, and bites the body of his neighbour. Because of this Paul utters the fearful saying, “If you bite and devour one another, take heed that you be not consumed one of another.” You have not fixed your teeth in the flesh, but you have fixed the slander in the soul, and inflicted the wound of evil suspicion; you have harmed, in a thousand ways, yourself and him, and many others, for in slandering a neighbour you have made him who listens to the slander worse; for should he be a wicked man, he becomes more careless when he finds a partner in his wickedness; and should he be a just man, he is lifted to arrogance, and puffed up; being led on by the sin of others to imagine great things concerning himself.
Besides, you have struck at the common welfare of the Church; for all those who hear not only accuse the supposed sinner, but the reproach is fastened on the Christian community; neither do you hear the unbelievers saying, “Such a person is a fornicator, or a libertine;” but instead of the individual who has sinned, they accuse all Christians. In addition to this, you have caused the glory of God to be blasphemed; for as His Name is glorified when we have good report, so when we sin, it is blasphemed and insulted!
Source: Homilies on the Statues (New Advent)