I live in an area of the country that knows what it means to be shunned. There are many in my church that have been shunned as they left the Amish church. They understand what it means to be rejected by their family. They understand what it means to be cut off so that every relationship they have ever known is gone. Over. Finished. They understand the loneliness that comes at that moment. They understand the gravity of their decisions. Because of this, the matter of excommunication in step four of church discipline, takes on a completely different significance where I live.
I believe in church discipline, but I do not believe in shunning. And I do not think Jesus does either. When Jesus refers to excommunication, He is NOT advocating shunning. In the fourth step of church discipline (Matthew 18:15-17), Jesus says that we are to treat them like a Gentile and tax collector. The Gentile would have been someone outside their covenant community. The tax collector was probably someone inside that had betrayed the covenant community. Treating someone outside your covenant community is NOT shunning.
How did Jesus treat the gentiles and tax collectors? How did He treat those that were outside the Jewish covenant community? He ate and drank with them. Not socially, but for a spiritual reason. He wanted to call them to repent of their sins. He loved them enough to continue seeking their spiritual restoration. It was not a casual relationship, but a very intentional one. He wanted to point out their sin, show them a solution, and call them to change.
To be sure, if a situation gets to step four in the process, there should be some marked difference in the relationship. But that difference should not be cold and indifferent. It is one that should be marked with the gospel truth of repentance.
There might be one exclusion to this. The Apostle Paul seems to make a case in 1 Corinthians 5 of sin so public and grievous that the only way to handle it is to send the person out of the community and not associate with them. Paul says to not even "eat with such a one" (1 Cor. 5:11). But the context of 1 Corinthians 5 is that the arrogance and spiritual pride of this sinning brother had so impacted the spiritual vitality of the church, that Paul calls for a separation. If someone's sin has caused the church to become desensitized to sin, then there probably needs to be a stronger separation.
Either way, the church should continue to pray for the repentance of that individual. There should be some in the church that continues to call them to leave their sin. But the relationship will be different.