Matthew 6:15 are Jesus' own words on how to deal with a sinner
15 “If your brother or sister[b] sins,[c] go and point out their fault, just between the two of you. If they listen to you, you have won them over. 16 But if they will not listen, take one or two others along, so that ‘every matter may be established by the testimony of two or three witnesses.’[d] 17 If they still refuse to listen, tell it to the church; and if they refuse to listen even to the church, treat them as you would a pagan or a tax collector.
Never once does it mention to shun them. Jesus sat down with tax collectors.
Luke 6:37 are also Jesus' words and says not to judge
37 “Do not judge, and you will not be judged. Do not condemn, and you will not be condemned. Forgive, and you will be forgiven. 38 Give, and it will be given to you. A good measure, pressed down, shaken together and running over, will be poured into your lap. For with the measure you use, it will be measured to you.”
Yet we have a "judicial" committee to judge a person.
So the scripture they use from 1 corinthians is totally against what jesus says. Maybe the apostle Paul was an early apostate? Ha, just my $.02