When is it permissible to boycott a person who commits a major sin?

The Shaykh : As for boycotting him, O my son, know that boycotting is a remedy. If it is beneficial, use it; if it is not beneficial or if it makes the situation worse, then leave it. Do you understand? So, if this man who lets his garment hang below the ankles straightens his conduct, feels ashamed, and says, "How can I be like the Samiri in the eyes of people, who said, 'No touching,' and then lifted his garment," then boycott him. But if boycotting him causes him to increase in sin, and he comes to dislike and hate you and incites people against you, then do not boycott him in that case. However, adopt this principle: boycotting is a remedy; if it is beneficial, do it, and if it is not beneficial, do not do it.