The word metzora means one who is afflicted with a certain skin disease (probably not leprosy, the usual translation). The rabbis take the word metzora apart and play with it, turning into motzi ra or motzi shem ra -- one who brings about a bad name (reputation) for someone else. So traditionally, this parasha is described as the symbolic punishment for one who engages in gossip.
I'm going to speak about gossip and lashon hara, literally "bad tongue", on Shabbat. Here is the first text I will teach, a defense of gossip I found in the voice of the narrator in Amoz Oz's novel Elsewhere, Perhaps. To be continued (and rebutted) on Shabbat in shul!
Whoever objects to such gossip betrays his own lack of understanding of our collective life [the narrator is referring to the 1950s kibbutz where the novel is set]. Gossip plays an important and respected role here and contributes in its way to reforming our society. In support of this claim, let us recall a statement we have heard made by Reuven Harish himself: the secret lies in self-purification. The secret lies in judging one another day and night, pitilessly and dispassionately. Everyone here judges, everyone is judged, and no weakenss can succeed for long in escaping judgment...We polish each other as a river polishes its pebbles...
...Gossip is simply the other name for judging. By means of gossip we overcome our natural instincts and gradually become better men. Gossip plays a powerful part in our lives, because our lives are exposed like a sun-drenched courtyard...Gossip is normally thought of as an undesirable activity, but with us even gossip is made to play a part in the reform of the world.