Christians are often accused of "judging" whenever they speak out against a sinful activity. However, that is not the meaning of the Scripture verses that state, "Do not judge." There is a righteous kind of judgment we are supposed to exercise with careful discernment (John 7:24). When Jesus told us not to judge (Matthew 7:1),
He was telling us not to judge hypocritically (Matthew 7:2-5).
If a believer sees another believer sinning, it is his Christian duty to lovingly and respectfully confront the person with his sin (Matthew 18:15-17) toward the goal of of bringing repentance in the other person (James 5:20) and restoration. We are to speak the truth in love (Ephesians 4:15), of course.
Teachers need to speak against sin. 2 Timothy 4:2 instructs us, "preach the Word; be prepared in season and out of season; correct, rebuke and encourage with great patience and careful instruction."
Revelation 2:2 "I know your works, your toil and your patient endurance, and how you cannot bear with those who are evil, but have tested those who call themselves apostles and are not, and found them to be false."
Galatians 2:11 "But when Cephas came to Antioch, I opposed him to his face, because he stood condemned."
1 Corinthians 5:1-13 "It is actually reported that there is sexual immorality among you, and of a kind that is not tolerated even among pagans, for a man has his father's wife. And you are arrogant! Ought you not rather to mourn? Let him who has done this be removed from among you. For though absent in body, I am present in spirit; and as if present, I have already pronounced judgment on the one who did such a thing. When you are assembled in the name of the Lord Jesus and my spirit is present, with the power of our Lord Jesus, you are to deliver this man to Satan for the destruction of the flesh, so that his spirit may be saved in the day of the Lord."
Matthew 7: 21-23 “Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but only the one who does the will of my Father who is in heaven. Many will say to me on that day, ‘Lord, Lord, did we not prophesy in your name and in your name drive out demons and in your name perform many miracles?’ Then I will tell them plainly, ‘I never knew you. Away from me, you evildoers!’
Psalm 37:30 "The mouth of the righteous speaketh wisdom, and his tongue talketh of judgment."
Amos 5:14-15 "Seek good, and not evil, that ye may live: and so the LORD, the God of hosts, shall be with you, as ye have spoken. Hate the evil, and love the good, and establish judgment in the gate: it may be that the LORD God of hosts will be gracious unto the remnant of Joseph."
Isaiah 59:8: "The way of peace they know not; and there is no judgment in their goings: they have made them crooked paths: whosoever goeth therein shall not know peace."
I Corinthians 1:10 "...be perfectly joined together in the same mind and in the same judgment."
Etc... etc... etc...
"And why beholdest thou the mote that is in your brother's eye, but considerest not the beam that is in thine own eye? Or how wilt thou say to thy brother; Let me pull the mote out of thine eye; and, behold, a beam is in thine own eye? Thou hypocrite, first cast out the beam out of thine own eye; and then shalt thou see clearly to cast the mote out of thy brother's eye." (Matthew 7:3-5)