Here’s a good article on this aspect of our faith:
Here’s a snippet:
Jesus told the Jews, “Do not judge by appearances, but judge with right judgment” (John 7:24).
He instructed his disciples what to do if someone sins against them:
Go and tell him his fault, between you and him alone. If he listens to you, you have gained your brother. But if he does not listen, take one or two others along with you, that every word may be confirmed by the evidence of two or three witnesses. If he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, let him be to you as a Gentile and a tax collector. (Matt. 18:15-17)
It is not possible to follow Jesus’ instructions without being “judgmental” of another’s behavior.
Paul, too, exhorted right judgment of other Christians: “For what have I to do with judging outsiders? Is it not those inside the church whom you are to judge? God judges those outside. Drive out the wicked person from among you” (1 Cor. 5:12-13).
Also, “Do you not know that the saints * will judge the world? And if the world is to be judged by you, are you incompetent to try trivial cases? Do you not know that we are to judge angels? How much more, matters pertaining to this life!…Shun immorality” (1 Cor. 6:2-18).
A look at the Old Testament reveals similar teaching: “You shall do no injustice in judgment; you shall not be partial to the poor or defer to the great, but in righteousness shall you judge your neighbor” (Lev. 19:15).
Clearly, contrary to what many would prefer to believe, the Bible exhorts us to rightly judge the behavior of others. The Catholic Church teaches likewise but cautions us just as Jesus did the disciples:
Respect for the reputation of persons forbids every attitude and word likely to cause them unjust injury. He becomes guilty:
of rash judgment who, even tacitly, assumes as true, without sufficient foundation, the moral fault of a neighbor;
of detraction who, without objectively valid reason, discloses another’s faults and failings to persons who did not know them;
of calumny who, by remarks contrary to the truth, harms the reputation of others and gives occasion for false judgments concerning them.
To avoid rash judgment, everyone should be careful to interpret insofar as possible his neighbor’s thoughts, words, and deeds in a favorable way: “Every good Christian ought to be more ready to give a favorable interpretation to another’s statement than to condemn it. But if he cannot do so, let him ask how the other understands it. And if the latter understands it badly, let the former correct him with love. If that does not suffice, let the Christian try all suitable ways to bring the other to a correct interpretation so that he may be saved.” (CCC 2477-2478)*