There is an unfortunate tendency in some sanghas to silence dissent by accusing dissenters of "wrong speech" when they would draw attention to misconduct by a teacher. Needless to say, a sangha that is experiencing this type of problem is already a sangha in trouble. The teacher is supposed to be a model of Buddhist ethical conduct and as such, an inspiration to the disciples. A teacher who fails to keep the precepts, whether a lay teacher or a monk who has many more vows to keep than the lay teacher, is one who is not fit to lead others.
"Distance yourself from Vajra Masters who are not keeping the three vows,
Who keep on with a root downfall, who are miserly with the Dharma,
and who engage in actions that should be forsaken.
Those who worship them go to hell and so on as a result."
---"Ornament for the Essence", by Manjushrikirti
The Sangha is a place of refuge, and therefore safety. If the guru is engaging in actions that cause harm to others, he is not only violating the sanctity and threatening the equanimity of the Sangha, he his risking turning current and future disciples away from the Dharma. In such a situation, drawing sangha members' and sangha directors' attention to the problem is the right path.
"When teachers break the precepts, behaving in ways that are clearly damaging to themselves and others, students must face the situation, even though this can be challenging. Criticize openly, that's the only way. Those who have been harmed by their teacher must take their complaint to the newspapers, and, if necessary, to the police."
---H.H. the 14th Dalai Lama
Examination of the words of the Buddha shows the correct interpretation of Right Speech and Wrong Speech. In a discourse with one of his disciples, the Buddha explains the guidelines.
"Potaliya, four kinds of people exist and can be found in the world. What kinds?
1) Some blame those who should be blamed, according to the truth, at the proper time, but do not praise those who should be praised, according to the truth, at the proper time.
2) Some praise those who should be praised, according to the truth, at the proper time, but do not blame those who should be blamed, according to the truth, at the proper time.
3) Some do not blame those who should be blamed, according to the truth, at the proper time, and do not praise those who should be praised, according to the truth, at the proper time.
4) Some blame those who should be blamed, according to the truth, at the proper time, and praise those who should be praised, according to the truth, at the proper time.
Potaliya, of all those four kinds of people, whichever blames those who should be blamed, according to the truth, at the proper time, and praises those who should be praised, according to the truth, at the proper time, this kind of person is the most beautiful and refined of these four kinds of people."
Here we see that the Buddha, contrary to what some would have us believe, does not advocate pleasing, truthful speech at the expense of unpleasant speech. Indeed, he exhorts us to criticize when criticism is due, if it is truthful and spoken at the proper time, according to the relevant circumstances. One can further understand his words to mean that silence in the face of danger or wrong-doing, would be wrong speech. He makes it clear that not blaming when blame is due is not an acceptable course of action. Elsewhere in his teachings, he instructs: "In the case of words that the Tathagata knows to be factual, true, beneficial, but unendearing and disagreeable to others, he has a sense of the proper time for saying them". Do not avoid speaking disagreeable but truthful and beneficial words, he instructs us, but be judicious in choosing the appropriate time to say them.
Compassion also serves as a guide in difficult situations. If there is the potential for harm in the sangha, does compassion not compel us to warn others of the danger? If we knowingly allow wrong-doing to continue, then we become complicit in violating the sanctity and the very purpose of the sangha, which is to provide a safe community of virtuous friends to support each other in their path to Enlightenment. Those who would defend a teacher who does not observe the precepts, and who harms others, "who keeps on with a root downfall", those are the enemies of the Dharma.