Church and Race

What would you say to a church leader who argued for geographical seperation of different ethnic groups because of the inevitable tension between them?
Who argued that the church's vision is spiritual and not social?

At the moment a bunch of us are thinking through the shrinking of the Anglican church in Sydney's south west.
Part of that has been looking at attitudes to race and immigration.
Both these attitudes above, and a support of limited immigration can be found in a short article on race by D B Knox.

While Knox is arguing that justice is the primary category that we need to defend, I wonder what his defence of racial separation has done for Anglican churches?