Matthew 7:1, Judge Not

Whenever someone does not like that you are making a moral judgment that condemns their actions, they love to trot out Matthew 7:1. "But Jesus says, 'Judge not, that you be not judged.'" Sadly, Christians are guilty of abusing this as well.

Author and apologist Greg Koukl has written a very good exposition of this verse.

     Here’s another example of applying [this tactic] to a passage that is almost universally misunderstood: “Do not judge lest you be judged” (Matthew 7:1). This is a verse everybody knows and quotes when convenient, even if they do not usually abide by the Bible. Jesus qualified this command, though, in a way that most do not:
     And why do you look at the speck that is in your brother’s eye, but do not notice the log that is in your own eye? . . . You hypocrite, first take the log out of your own eye, and then you will see clearly to take the speck out of your brother’s eye. (Matthew 7:3, 5)
     A closer look at the facts of the context shows that Jesus did not condemn all judgments, only hypocritical ones — arrogant condemnations characterized by disdain and condescension. Not all judgments are of this sort, so not all judgments are condemned. In fact, even in this passage Jesus actually encourages a different sort of judgment once the hypocrisy has been dealt with (“first take the log out of your own eye, then you will see clearly to take the speck out of your brother’s eye”).
     Koukl, Gregory (2009-05-19). Tactics: A Game Plan for Discussing Your Christian Convictions (Kindle Locations 2847-2856). Zondervan. Kindle Edition. 

D.A. Carson also has a very good devotional on the passage.

There is a difference between judgment, hypocritical judgment, and judgmentalism.