The early Christian church, movement, in its scriptures shows that it had teachers and that this was by the will of God. Within this movement, they were told to judge their brothers and sisters' behavior:
1 Corinthians 5:11-13: But now I am writing YOU to quit mixing in company with anyone called a brother that is a fornicator or a greedy person or an idolater or a reviler or a drunkard or an extortioner, not even eating with such a man. 12 For what do I have to do with judging those outside? Do YOU not judge those inside, 13 while God judges those outside? “Remove the wicked [man] from among yourselves.”
Here it is clearly stated, that God, not Christians, judge those on the outside; though various acts naturally may be condemned as Paul does in the above scripture.
Christ himself spoke harshly against the religious leaders of the time. The quote you mention clearly says, though, for Christians to be careful of how they act, judge, for the judgment they give others will be used against themselves if they are guilty of the same sin. Thus, don't judge a thief for being a thief, if you yourself is a thief - that is the point. Another important point here, which many ignore, is not to be busybodies in other people's lives judging them for their choices in their lives that truly belongs to the individual. Such busybodies are even put in the same categories the wicked.
If then I use scriptures to show what (the believer accepts) God has inspired to be good or wicked, if I am true to the spirit of the text, the harmony of the text - it is then not really I who speak, but God who says this, though I might be the one to find it for the person being taught.
It is unfortunately true that many churches and individuals claim this or that to be a sin, while scripture in no way says this. The person who receives teaching / admonishment / assistance must then be on the lookout to check if indeed what is stated is according to scripture and not just some church teaching.