While derogatory information may be related for a constructive purpose, slander cannot be justified. One does not have the right to exaggerate or alter facts for a constructive purpose, nor may one omit details that minimize the severity of the person’s actions. (Conversely, one must omit authentic details that make the story sound even worse if the result can be attained without their being mentioned.)
Sefer Chofetz Chaim, 17 Cheshvan, page 142
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