If you see someone is wrong, you should not let your disapproval become an obsessive hate. Rebuke them if necessary and save them from Divine punishment or, according to another view, save yourself from a share in their sin by appearing to acquiesce in what they are doing.
Some make criticising others an art form. They are so good at telling others off that they think they are God’s policemen. Rabbi Elazar ben Azariah said, “I wonder if there is anyone in this generation who knows how to reprove” (Arachin 16b). To utter reproof you must speak out of love, not hatred. You must be fair and constructive, and not so negative as to lose all credibility; and you must be without sins of your own.
Rabbi Tarfon says that if you tell someone, “Remove the mote from between your eyes,” he might retort, “Remove the beam from between your eyes!”
These principles apply to rabbis too. Simeon Singer, a great Anglo-Jewish minister of an earlier generation, said that rabbis should avoid hellfire and brimstone sermons; he pointed out that the curses of the Tochechah are read only twice a year, and one of those times is in the English summer when people are away on holiday anyhow.
Some Chassidic teachers opposed all sermons; they said that whilst rabbis were permitted to teach, they should not admonish. They added that if a rabbi teaches well and his congregation take note, no rebuke will be necessary.