RESPONSE - First, let's take a look at what God was telling David when he made that statement. David was there to take Saul's life!  He was gonna kill him but God said no.  God did not want David to kill Saul because he was his successor and had he murdered Saul, he would have set a precident of murdering leaders to take the thrown.  God told him to "touch him not" but what he was saying was that he didn't want David to murder him.  Yet there are some obvious factors here that must be brought out to fully understand.  It's obvious that David had already been discussing Saul's error to his men because they were there with him when he went to kill Saul.  So, David had already warned his people of Saul's error.  Even though he loved Saul, he was prepared to kill him for the sake of right.  He knew that Saul wasn't right and he taught his men that Saul was not right.  All throughout the scripture, God raised up prophets, apostles, and leaders that exposed deceit and carnality in the body of Christ.  There has to be judgement passed on believers based on their actions as well as their intent.  Not eternal judgement, but judgement in the sense of sorting out the truth based on the Word of God.  The bible says that whether it be a prophet or an angel, if they teach contrary to the Word, let them be accursed! 

PROOF - In 1 Corinithians 5, Paul judged a man based on this actions and this man was not present!  Paul called him out and asked for his removal from the church without him even being present.  What does this teach us? It teaches us that we do not judge the world, but we are judges of the body of Christ.  We use discernment to look into things and we use the bible to "try every spirit" as the Word says.  We go to our brother in secret when he sins secretly or discreetly.  But we go to the public when heresy and public sins are commited.  Don't try to use your flesh to understand this.  You must born of God and really a total bible believer. 

SCRIPTURE - 1Tim. 5:20 Those who continue in sin, rebuke in the presence of all, so that the rest also may be fearful of sinning.