Halakhah su Levitico 25:17

And this entire issur of lashon hara applies only [when spoken] against the man who is in the category of "your neighbor" [amitecha], "am she'techa," "a people who is with you" in Torah and in mitzvoth. But those people whom he knows to have "apikorsoth" [heresy] among them, it is a mitzvah to demean and to shame, both in their presence and not in their presence, in everything that he sees or hears about them. For it is written (Vayikra 25:17): "And you shall not wrong, one man, his fellow [amito]" and (Vayikra 19:16): "You shall not go talebearing among your people [be'amecha]." And they are not in this category, for they do not act as Your people. And it is written (Tehillim 139:21): "Do I not hate your haters, O L–rd? And against those who rise up against You do I strive." And one who denies the Torah and prophecy of Israel, both the written and the oral Law, is called an apikoress [heretic], even if he says all the Torah is from Heaven, except for one verse, or one kal vachomer [a fortiori argument], or one gezeirah shavah [identity deduction], or one dikduk [inference].

And all of these dinim that we have set down apply only to a man who is wont to regret his sins. But if you have probed his ways and seen that the fear of G–d is not before his eyes and that he always persists in a way that is not good — such as one who divests himself of the yoke of Heaven or is unheedful of a transgression which every one of his people knows to be a transgression — that is, whether the sin you wish to reveal has been committed deliberately many times by the sinner or he often transgresses deliberately a different sin which is known by all to be a sin — then it is apparent that it is not because his evil inclination overpowered him that he transgressed the word of the L–rd, but that he does as his heart sees fit and the fear of G–d is not before his eyes. Therefore, it is permitted to shame him and to speak demeaningly of him, both before him and in his absence. And if he does something or says something which can be judged either in the scales of merit or in the scales of guilt, he must be judged in the scales of guilt, since he has shown himself to be an absolute evildoer in his other affairs. And thus have our Rabbis said (Bava Metzia 59a): "'And you shall not wrong, one man, his fellow [amito]' (Vayikra 25:17) — 'a people who is with you' [am ito] in Torah and mitzvoth — do not wrong him with words!" And if one does not direct his heart to the word of the L–rd, it is permitted to shame him for his deeds, to make known his abominations, and to spill scorn upon him. And they said further (Yoma 86b): "Flatterers are exposed because of the desecration of the Name [that they engender]." And much more so if one reproved him for [his sin] and he did not desist from it, is it permitted to expose him and to reveal his sin in "the public gate" and to spill scorn upon him, until he returns to the good, as the Rambam has written in the end of Hilchoth Deoth 5. But it is important not to forget certain considerations that this entails, which I have written of in Be'er Mayim Chayim.

(13) And many times another negative commandment is transgressed. For very often one's friend is demeaned for his early deeds, for a family trait, for the paucity of his learning, or for his [mediocre] work, each man according to his situation, things being said to him which anger and confound him and against which he has no defense. Even if this transpired between the two of them alone [no one else being present], he [the speaker] transgresses (Vayikra 25:17): "And you shall not wrong, one man his fellow," which refers to verbal wronging (viz. Bava Metzia 58b). How much more so if this occurred in the company of others! It emerges, then, that if one slights his friend both through rechiluth or through lashon hara, before him alone or before others, aside from transgressing the negative commandment of lashon hara and rechiluth, as stated above, he also transgresses this negative commandment.