Parashat Tazria contains the rules of the punishment Tzaraat. Commonly (mis)translated as leprosy, this is usually associated with the grave sin of Lashan HaRa. The Parasha explains in detail many of the rules of Tzaraat, including the rules that the Kohen needs to follow upon examining someone who is suspected to have Tzaraat. In this vein, the Pesukim state, “VeIm Paso Yifseh HaNetek BaOr Acharei Tahorato VeRaahu HaKohen VeHinei Pasah HaNetek BaOr Lo Yevakeir HaKohen LaSeiar HaTzahov Tamei Hu,” “But if the affliction shall spread on the skin after he [the person suspected of having Tzaraat] has been declared pure, the Kohen shall look at it and behold the affliction has spread on the skin, the Kohen need not examine it for a golden hair [one of the signs of Tzaraat], he is Tamei” (VaYikra 13:35-36).
One of the rules in the Halachic legal system is that once a person is declared innocent, his case cannot be reopened, even if the crime in question was that of murder. Why do the laws of Tzaraat seem to contravene this rule? The Pesukim seem to teach that even once a person is confirmed clean of Tzaraat, the Kohen can return and decide that he actually does have Tzaraat! Moreover, these Pesukim specifically state that the Kohen doesn't even have to look for all the signs of Tzaraat before declaring someone Tamei in this situation. Doesn't this violate the spirit of judging people favorably (see Avot 1:6)?
An answer is that these Pesukim show how bad Loshon HaRa truly is. The fact that the gossiper’s case could be reexamined while that of a murderer can not shows that Lashon HaRa is one of the worst sins, worse than murder (see Arachin 15b regarding the severity of Lashon HaRa). More so, these Pesukim show the concept of “measure for measure.” The person was afflicted with Tzaraat in the first place because he didn't judge people favorably, which led him to speak disparagingly of them. Therefore, when he is being examined to determine whether or not he has Tzaraat, he isn't judged favorably either.
We must all work to stop Lashon HaRa in its tracks. The Chafeitz Chaim in his epochal work Sefer Chafeitz Chaim notes that the Gemara (Yoma 9b) states that the second Beit HaMikdash was destroyed because of Sinat Chinam, baseless hatred. The Chafeitz Chaim explains that the Gemara means to include Lashon HaRa, for Lashon HaRa causes divisiveness to reign amongst people and is a prime cause of Sinat Chinam. If we wish to see the Beit HaMikdash rebuilt, we must first eliminate the cause of its destruction, the terrible sin of Lashon HaRa.