Zanakis was found guilty of extortion, but only after he had gotten away with another scam. However, in most of these cases the plaintiffs are, to some degree, in the right. Matt Drudge's accusation that Sidney Blumenthal was a wife beater was false, although Blumenthal's suit gave the accusation far more circulation than it would have gotten otherwise. Alonzo Jackson really had bought the shirt he was accused of stealing. Matthew Fogg could well have been the victim of discrimination.
Criminal prosecutors operate within certain restraints.
A prosecutor can't seek the death penalty for shoplifting. Naval aviator Paula Coughlin may not have shot down any enemy planes, but she managed to nail Hilton Hotels for a five million dollar sexual harassment judgement, upheld on appeal. Law enforcement agents seem to have a particular proclivity for the courtroom. Not only are Fogg and his fellow marshals all suing, but they may run into quite a few FBI agents on the way to court. One FBI agent was found to have embezzled money from the agency.