Even though one must not accept lashon hara [slander] still one is obligate to be careful that "perhaps it is true." The Hafetz Haim [Rav Meir Hakohen] goes into this in detail but in any case the surprising thing is that being חושש [being careful on the side of caution] is an obligation. He brings this from Tractate Nida [page 61] with the verse "the people that were killed by Gedaliah". The Gemara explains that Gedaliah should be been careful on the side that perhaps it was true that Ishmael ben Korah wanted to kill him.
There is an argument over there in Nida between Tosphot [in the name of Rav Ahai Gaon] and the Maharshal about this law.
In any case, one must be careful on the side that the Gra was correct for signing the letter of excommunication, even if one thinks it was mistaken.
[That is nowadays it has become clear that it was not a mistake; and everyone that thought the Gra was wrong were the ones who were mistaken.]
In the laws of חרם excommunication we find not to learn from the person who has been excommunicated. So why are they still quoted?
[Incidentally, according to the actual phrasing of the letter, Rav Nahman of Breslov is not included in the excommunication.]
There is an argument over there in Nida between Tosphot [in the name of Rav Ahai Gaon] and the Maharshal about this law.
In any case, one must be careful on the side that the Gra was correct for signing the letter of excommunication, even if one thinks it was mistaken.
[That is nowadays it has become clear that it was not a mistake; and everyone that thought the Gra was wrong were the ones who were mistaken.]
In the laws of חרם excommunication we find not to learn from the person who has been excommunicated. So why are they still quoted?
[Incidentally, according to the actual phrasing of the letter, Rav Nahman of Breslov is not included in the excommunication.]