1. Nothing in this passage limits the sin to certain kinds of offenses deemed particularly serious.
2. A lot of minor offenses can easily just be overlooked, for the sake of keeping that same peace.
3. The different meanings of “witnesses” in English cause unnecessary confusion.
4. There really isn’t any way to make “tell it to the church” mean “tell it to the pastor” or “tell it to the elders” or some other subgroup of the church.
5. Treating someone like “a pagan or a tax collector” means treating them like a non-Christian.
Read the rest of Blomberg’s remarks here.