There is no loyalty greater than loyalty to Truth, to the best of our imperfect human ability to approximate what that is. Are you omniscient, all knowing, all seeing? Knowledge of Truth – with a capital T, whole and complete – is not a human capacity.
Integrity requires that your first loyalty be to truth – loyalty to a mere human being pales in comparison.
When our interpretation of loyalty to a person allows harmful actions by that person to go unacknowledged, we do a disservice both to that person and to the object of harm. Our silence deprives the person making harmful choices of a possible learning experience, as well as making ourselves co-conspirators (co-dependent enablers) in the harm itself.
Speak up when someone says or does something harmful to others.
No amount of valuable service or significant contribution justifies shielding a person from dealing with – and correcting – harmful choices.