Libel is a crime because words can, and often do, cause real damage to peoples' lives: their reputations, thence their abilities to make a living, etc. I can lie about you all day long to your friends and family and coworkers, and no doubt many of them won't believe it, but sooner or later someone will, and then someone else, and pretty soon you become a person about whom many folks have doubts. And who knows, you may turn into one of those doubters. It's fine to think you're strong enough so that my words could never hurt you, but that attitude simply belies immaturity & inexperience.