The silencing effect that the threat of a libel lawsuit can have on those who would be sued if they continue such speech. The whistleblower's silence after being threatened with a lawsuit by her former company is a classic case of libel chill.
Prov. It is more offensive to say something damaging and true about someone than it is to tell a damaging lie. Jill: Fred's really upset. Someone's started a rumor that he's unfaithful to his wife. Jane: But it's true. Jill: Yeah, but the greater the truth, the greater the libel.