I know what you are thinking; the Word tells Christians not to judge (Matt. 7:1; Rom. 2:1; 14:10, 13; 1 Cor. 4:5; Jam. 4:11-12). On the other hand, the Scriptures also teach us that Christians are to act as judges in this life, and in the life to come.
In this life, we are to judge the behavior of other believers and make every effort to get them to repent. Matthew 18:15-18, Jesus teaches His disciples the steps Christians are to take in correcting a brother or sister. You are to go to the person privately and try to persuade him to change the behavior (v. 15). Should he reject your counsel, then you are to take one or two others with you to try to reason with the offender (v: 16). I do not believe this is permitting us to gossip or to seek "reinforcements." I understand Jesus to be telling us that we are to have witnesses who observe our effort to persuade the person to repent. In other words, they watch you make a second effort to reason with the offender. They in turn, should the person still not repent of the offensive behavior, are to stand with you as you present your concerns to the entire assembly (v. 17). While individuals are encouraged by the Lord to warn the person, the responsibility for judging the person is that of the entire local church (v. 17-18).
The Apostle Paul clearly taught that the Church at Corinth was guilty of failing to judge the improper behavior of one of its members (1 Cor. 5:1-8). Not only had they failed to rebuke the offender, they actually saw his behavior as an example of the liberty of Christians, who are no longer bound by the Law (v. 2, 6). Paul, himself, did not hesitate to judge the behavior, as he literally sentenced the offender to physical death (v. 4-5). Even in this case, Paul desired that the individual would repent (2 Cor. 2:1-10). Paul also taught that Christians are to judge themselves as individuals who are accountable for their words and actions (1 Cor. 11:28-31). He even told them that they should judge him, and every teacher of God's Word (1 Cor. 10:15 - also see Acts 17:11).
In the life to come, when we have received the character of Jesus Christ, we will judge both men and angels (1 Jn. 3-2; 1 Cor. 6:2-3). Because we do not know whether or not a brother will repent or the lost will accept Christ later in life, we are not to condemn (write-off) others. The main difference between the judgment we are to exercise in this life, and that in the life to come, is here, we are to make the effort to produce repentance, and there, we will be condemning the lost and the fallen angels to eternal separation from God. Until I am like Jesus, I think I will stick to focusing my judging to that of judging myself. I will ask myself two questions, "What Would Jesus Do?" and "Is what I am about to do going to bring glory to God?" I can't go wrong with either, because they are really the same thought using different words.