Is fulfilling a trust obligatory even when aware of its potential harm?

Abusing a Muslim is a sin and an act of wickedness, as stated in the Hadith (definition): "Abusing a Muslim is wickedness (fisq) and fighting him is disbelief (kufr)." The perpetrator of such an act is wicked (fasiq). Delivering messages that contain abuse and insults to people is a form of cooperation in sin and aggression, which Allah has forbidden in His saying: "And do not cooperate in sin and aggression." It is not fulfilling a trust, because a trust is that which is obligated to be fulfilled by religious law.