Lashon Hara L'Toeles

A certain group of students were learning in a yeshiva in Israel that was known as an environment where false dei’os flourished. These students knew that the only way to convince their fellow students of the folly of such opinions was to speak against the rabbis who championed such opinions. But they wondered if this was halachically permitted. After all, talking against a talmid chacham is a very serious sin.
To their surprise, when they went to the Chazon Ish, zt”l, and asked him if this was permitted he refused to answer them. They decided to return a second time but the Chazon Ish was silent yet again.
On their third visit, he began to ask them numerous questions “What are your names? Where are you from? How long have you been learning?”
When he was finally satisfied with their answers he said, “In terms of the halachos of a talmid chacham... Although the rabanim you have named have a position, they do not learn every free moment. The Chofetz Chaim rules that only one who knows how to learn and whose Torah study is his exclusive occupation is a talmid chacham. These people are like tailors and shoemakers that work to earn a living.
“But that’s only regarding the question of whether disparaging these particular rabbis constitutes embarrassing a talmid chacham. If you spread negative opinions about them, you will still violate the prohibition of lashon hara. You wish to speak l’toleles? Let me tell you how to speak lashon hara l’toeleles. Rav Chaim Brisker only attended the first Agudah convention because, during the proceedings, someone spoke against a certain communal activist and claimed that something he had done had caused trouble. Rav Chaim immediately stood up and proclaimed, ‘It is prohibited to sit here since people speak lashon hara!’
“But why was this lashon hara?” asked the Chazon Ish. “The person speaking was addressing an important concern and every word he spoke was absolutely true. It was forbidden because the person spoke in a judgmental and self-righteous manner. If the speaker at the convention had said instead, ‘Rabbosai! This person’s error has brought about a terrible problem! Let us all work together to try and rectify it!’ this would have been lashon hara l’toeles.”