From Christine Korsgaard, “CREATING THE KINGDOM OF ENDS: RECIPROCITY AND RESPONSIBILITY” (Philosophical Perspectives, 6, Ethics, 1992), p.323
Another kind of consideration comes from Kant’s iterated demand, in the Metaphysical Principles of Virtue, for generosity of interpretation. As I mentioned at the beginning of my discussion, Kant believes that we cannot know people’s most fundamental or intelligible characters. But he censures contempt, calumny, and mockery as much for their disrespectful and ungenerous nature as for their lack of a theoretical basis. (MMV 462-468/127-133) He says, for instance, “One should cast the veil of philanthropy over the faults of others, not merely by softening but also by silencing our judgments.” (MMV 466/132) Our theoretical estimate of another person’s character may be set aside in favor of our respect for the humanity within him. The reproach of vice, according to Kant,
…must never burst out in complete contempt or deny the wrongdoer all moral worth, because on that hypothesis he could never be improved either-and this latter is incompatible with the idea of man, who as such (as a moral being) can never lose all predisposition to good. (MMV 463-464/129)
(my bold)
Let us, in this life, speak softly and carry no stick at all. This is the Buddhist precept of right speech. This is not to say that we should remain silent in full, but only that our words must be meant to help, to clarify error, to shed light onto darkness. We can judge actions as best as we can from our limited perspective, but human beings, as they are deeper than their mere past actions, cannot be judged in themselves.