The Apostle Paul says that if they take communion, they are eating and drinking damnation unto themselves. I Cor. 11:29
I agree with you in principle. But note that Matthew 18:15-17 shows that Jesus taught that a Christian congregation is to ultimately kick unrepentant sinners out of the congregation.
In fact, 1 Corinthians 5 is an example of Paul basically telling that church to do what Jesus had taught as it concerns a sexual offender.