The tongue is an awesome weapon. It can destroy people's lives and reputations. It can create divisions between people and tear apart entire communities.
But there are times when even gentle, respectful people have to resort to words as a weapon: in self defense.
People sometimes inflict real harm on others -- sometimes financial, sometimes physical or emotional. There are many situations where the desired course is to forego our presumed rights in a dispute or to overlook the hurt which we have suffered -- for the sake of peace, and so that we may rise to the lofty levels which the Torah seeks of us. But this is by no means a blanket principle, because the Torah does not want us to become victims of exploitation or abuse.
When a strong self-defense is called for, the Torah places the weapon of words at our disposal, with careful instructions on how to use them.
The Chofetz Chaim explains:
We have learned in the previous segment that if someone has wronged me, I am forbidden to tell others of his misdeed for the constructive purpose of influencing him to correct his behavior. This is because we must assume that my true intention, at least partially, is simply to derive satisfaction from having others know of the wrong which was committed. However, says the Chofetz Chaim, I would be permitted to tell others what happened if this will help to have the wrong corrected. For example, if someone steals from me, and I can influence him to return the money by speaking to his parents or rav (rabbi) and convincing them of my case, then in most instances, the Torah will allow me to pursue that course of action.
Another example would be in the case of verbal abuse or physical harm. If someone has hurt me in such ways, and is likely to continue doing so, I can tell my story to those people who are in a position to convince the abuser to stop.
The same would apply if I were to learn that someone is planning to harm me and I can thwart his plans by speaking to the appropriate party. The words spoken in an effort to enlist help in these situations are permissible, though they denigrate the abuser. Halachah permits them in the guise of self-defense, as a shield and not a sword.