Perhaps you have noticed that the order in which we've considered these types of peer pressure and the possible responses goes from best to worst. The best case scenario is when our companions encourage us to do that which is right and we do it. When our companions start encouraging us to do wrong, hopefully we will still continue doing that which is right and we will find new companions. The real problems start when our companions pressure us to sin and we succumb to their pressure.
However, I believe that the fourth case is the worst of the four. When our companions encourage us to behave righteously, that is good, but if we fail to heed their advice and commit sin then our attitude is improper. In such circumstances we are rebellious toward God and His truth. When I am being encouraged to do that which is right by my peers, yet I choose to disregard their words, I'm living as a rebel before God.
There are several biblical examples of this sort of tragic rebellion. Consider what Paul stated regarding Demas, Hymenaeus, and Alexander, for instance: II Timothy 4:10 - "For Demas has forsaken me, having loved this present world..."; I Timothy 1:19,20 - "Having faith and a good conscience, which some have rejected, concerning the faith have suffered shipwreck, of whom are Hymenaeus and Alexander, whom I delivered to Satan that they may learn not to blaspheme."
In the early church, when a Christian manifested an attitude of rebellion toward God and His word, the church was to withdraw fellowship from him or her. In other words, when a child of God chose to live in sin and refused to repent or heed the exhortations of other Christians to do right, the church was to sever their social interaction with the rebellious one. This is what the Lord had divinely instructed. They were to no longer have anything to do with that person--except admonish the individual to turn from his or her sins and come back to God (II Thess. 3:14,15).
This form of congregational discipline is a type of peer pressure. It is intended to get the erring to come to his senses and repent (e.g., I Cor. 5; II Cor. 2:3-11). It is also designed to keep the church pure.
In the Lord's church today, are there ever times when a congregation should withdraw fellowship from an individual or group of people? The answer is yes. When Christians are walking disorderly (i.e., out of step with the Lord and His word), they need to be withdrawn from if they will not turn away from the paths of wickedness and turn to the way of righteousness (cf. II Thess. 3:6ff). We must exert pressure upon unfaithful brethren to repent before it is everlastingly too late!