"if they don't repent, put them up front on the church stage in the spotlight to shun and excommunicate them in front of thousands"

Brian Dodd on Matthew 18's"tell it to the whole church":

Step 3 involves a larger group of 10 or 20: "If they won't listen, tell it to the gathering." The Greek for "church" is "gathering," and this usually happened in homes in the New Testament period, and surely did not involve the modern conception of a stage/performance/spotlights. Jesus is not talking about an auditorium where you shame and shun someone, but a living room where you have a family meeting.  link, full article