"If he will not listen to the Church, treat him as a pagan or tax collector." --Jesus.
Sometimes we Catholics wonder the same thing.
Probably because you leave out the FIRST part of the story:
Matthew 18:15-17 (NIV)Dealing With Sin in the Church
15 If your brother or sister sins, 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. 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.
It's interesting that you'll use the BIBLE to try to make a point; and yet ignore other stuff.
ACTS 2:42-4444 All the believers were together and had everything in common.
45 They sold property and possessions to give to anyone who had need.