The idea behind lust and calling someone a fool is not about thought policing. Although taken to the extreme that is exactly what is produced. Rather, it is an insight into behavior. Some people do things spur of the moment or on a whim. On the other hand, many people do things and thoughts proceed them.
If someone were to be blamed for thinking, then the point of the illustration was missed entirely. What then was the real point? Imagine if you will a situation where someone does nothing outwardly illegal, yet feels justified in internally hating the undeserving. There is nothing legally wrong, and it can be assured that thought policing is wrong, but not only do thoughts make actions more likely, thoughts can destroy the person who think as well.
The illustration is not to say that lust = adultery or that 'you fool' = murder. To say that it is cannot be more superficial an understanding. Instead, it is a call towards the importance of thought-life. But importance does not mean condemnation. For even if lust = adultery, which it surely does not, did Jesus condemn the aduteress? Pay heed then!
Again, we may take the example of the Pharisee whom Jesus alluded to as white washed tombs... clean on the outside wanting on the inside. Again, thought policing is not the key! We can understand this through its opposite... the prostitutes, lepers, tax collectors, etc whom Jesus accepted. Although society rejected them, it is said that God exalts them because the have sought after him. What does this mean? It isn't that your thoughts betray you, it is that putting on a show for everyone about self-righteousness is merely that. What does it benefit a person to be known by all to have good qualities yet himself lack them in truth? Like a person who stole the answers to a test without studying... no one knows but what is missing cannot be denied!
) and you are fully conscious, of whats happening.
