Many people like to jump on Christians and condemn them for being "judgemental" by throwing out "Do not judge, or you too will be judged." However, brief look at the context of that verse will yield a more thorough interpretation.
Matthew 7:1-5The admonition here is not that we should never judge between good and evil, but rather that we should approach judgement cautiously and humbly, aware that we will be held to the same standard we apply to others.
"Do not judge, or you too will be judged. For in the same way you judge others, you will be judged, and with the measure you use, it will be measured to you.
"Why do you look at the speck of sawdust in your brother's eye and pay no attention to the plank in your own eye? How can you say to your brother, 'Let me take the speck out of your eye,' when all the time there is a plank in your own eye? You hypocrite, first take the plank out of your own eye, and then you will see clearly to remove the speck from your brother's eye.
Further, there are three aspects of justice. The first, reserved to God, is the right to set the rules and lay down the definitions of right and wrong. When man usurps God's authority to make the rules (or expands on the rules God has made) he engages in what is often called legalism -- a practice Jesus soundly denounced.
Luke 11:46Once the laws have been established, each individual action must be held up to the light and examined to determine whether it is good or evil; this is the second aspect of judgement, and God entrusts it to us, imperfect though we are.
Jesus replied, "And you experts in the law, woe to you, because you load people down with burdens they can hardly carry, and you yourselves will not lift one finger to help them."
Romans 12:9This discernment requires wisdom, as it's easy to mistake our own predilictions for God's perfect standards. Nevertheless, it makes no sense to command us to "hate evil" and "cling to good" if we're not able to classify the concrete experiences of our lives into these abstract categories.
Love must be sincere. Hate what is evil; cling to what is good.
Our responsibility to judge is restricted to the application of God's laws. If we see someone murder, we are right to condemn him for breaking God's law. If, however, we don't like blue hats and decide to condemn blue-hat-wearers, we become a law unto ourselves and put ourselves in God's place.
The third part of justice is perhaps the most complicated: the execution of punishment. God delegates earthly punishment to governments -- who are required to act justly -- and reserves the determination of eternal punishment for himself.