durangodawood-
Jesus himself identified certain actions and motivations as 'unclean,' and so not to be entertained:
He went on, "What comes out of a man is what makes him 'unclean.' For from within, out of men's hearts, come evil thoughts, sexual immorality, theft, murder, adultery, greed, malice, deceit, lewdness, envy, slander, arrogance and folly. All these evils come from inside and make a man 'unclean.' (The Gospel of St. Mark 7:20-23,NIV)
This kind of behavior Jesus did not approve of, nor were his disciples to approve of such behavior. These 'uncleannesses' also have one thing in common; they all require that the person deliberately focus on them. Unlike 'stumbling along the way' as other shortcomings would involve, these needed for the attention of the person entertaining them to be focused on them as a conscious state of mind, and even a plan of action.
We need to remember that the vast majority of Jesus' teachings, including the admonition not to judge, were directed at fellow Jews. As such their society was an extremely legalistic one, so much so that they even charged Jesus himself with violating the Sabbath because he healed on that day. Under their legalism that commandment alone had over 1,000 laws attached to it, and certain sects taught that in order to obey that one commandment as it should be obeyed, every one of those 1,000+ laws needed to be obeyed.
With such a society it was not enough to simply tell them to lighten up. Jesus had to take them the other way. In 1965 I heard a rabbi describe it as bending a reed in the opposite direction as far as it was originally bent in order to cause it to eventually straighten. It would not be enough to bend that reed just to the point where they wanted it to be, namely, straight. They would have to bend it past the straight point in the opposite direction as far as it was originally bent in the other direction. Only then would it return to its correct point.
Jesus applied the same logic to his society. They were extremely legalistic, with everyone nitpicking. The way to correct that was to forbid them to judge anyone. Following that absolute ban on judgementalism their society would return to the point where they should be.