This is what the Pharisees were guilty of. They could see everybody else's sins but not their own. Jesus is teaching we do need to be careful of how we do judge - Matt. Blessed are the merciful, for they shall obtain mercy. For judgment is without mercy to the one who has shown no mercy.
Mercy triumphs over judgment.
The standard we judge by cannot be our opin ion or our feelings. For I am not ashamed of the gospel of Christ, for it is the power of God to salvation for everyone who believes, for the Jew first and also for the Greek. Let my tongue sing of Thy word, for all Thy commandments are righteousness. We are forbidden to be involved in hypocritical judgment, but we are commanded to make righteous judgment according to the Word of God. We can't tell just by looking at their appearance.