He goes on to consider the puzzle of how refraining from speaking truth could be a good thing for Christians, who consider themselves people of Truth, and comes up with a number of reasons for refraining from detraction. I'm interested in the second and fifth points:
We are all sinners. By disclosing a hidden fault of another, we make it seem like this person is worse than all the people whose hidden faults are not disclosed. Frequently, the person is made to seem worse than the detractor. There is, thus, an injustice when there is no special reason to disclose the sins of this individual.It's good to have a word for this thing I do too often.
[...]
When the faults of another are disclosed to sinful humans, these humans will be tempted to take an inappropriate attitude towards these faults, an attitude of judgment rather than forgiveness. Thus, detraction is not only a sin against the person whose reputation is being unjustly tarnished, but also a sin against the listener who is being tempted into sin.