Please explain "objectively valid reason"

The CCC has this about respecting the reputation of others:
2477 Respect for the reputation of persons forbids every attitude and word likely to cause them unjust injury. He becomes guilty:
–of rash judgment who, even tacitly, assumes as true, without sufficient foundation, the moral fault of a neighbor;
–of detraction who, without objectively valid reason, discloses another’s faults and failings to persons who did not know them;
–of calumny who, by remarks contrary to the truth, harms the reputation of others and gives occasion for false judgments concerning them.

In order to understand and put this into practice, I need to know what constitutes an “objectively valid reason” and specifically how we should understand “objectively.” (I looked it up in the dictionary, but so far that hasn’t helped to answer this question.)

Would it be accurate to say it is not detraction, and it is morally acceptable, if it is necessary to speak up in order to prevent a greater harm? As a fictitious example, imagine you discovered that one of your neighbors had a criminal record as a child molester. Would it be morally acceptable to privately disclose it to neighborhood parents so that they could take measures to protect their children?

What about using someone’s behavior as an example to teach others? For example, you might say “That person is living in sin and God will punish him. My friends, let us not live like him.” Then, when he dies we may say “He lived in sin, but remember, we must not speculate about his final judgement. He may yet have repented. Let us remember that God’s mercy endures forever.”

Is it more acceptable if the person is a public figure, like a politician or movie actor?

Is it more acceptable if the person is far away and relatively unknown, so that he is unlikely be affected by our disclosure of his faults and failings?

Is it more acceptable if the person has been dead a long time, like fifty years, so that our disclosure would have no direct impact on him or on anyone now living? In this case, is there such a thing as “presumed consent,” in which we may presume that the person would consent if he knew it would be of value as a lesson to others?

It would appear to me, that to caution a person, because of known facts about a business that was known to be dishonest to prevent that person from being a victim of the dishonesty
would be an objectively valid reason. If it were just opinion, it would be another matter.
What makes it objective, is that it exists in reality, and not a product of imagination, or opinion. Also, to use charity as a guide in our attitudes, opinions, and statements is always a moral necessity in guaranteeing our proper behavior, and to avoid sin.

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