The First Amendment protects people against much more than criminal prosecution. Cases I recommend you read include:

Hustler Magazine, Inc. v. Falwell, 485 U.S. 46

Simon & Schuster, Inc. v. Members of New York State Crime Victims Board, 502 U.S. 105

The New York Times v. Sullivan, 376 U.S. 254, 84 S.Ct. 710, 11 L.Ed.2d. 686 (1964)

Gertz v. Robert Welch, Inc., 418 U.S. 323, 94 S.Ct. 2997, 41 L.Ed.2d. 789 (1974)