"Actually, that only works if one buys into the Ronald Reagan/Margaret Thatcher concept of a "Free Market Economy" where you have ever expanding markets requiring ever expanding populations to support them."

Richards comment wasn't a theory that needs justifying, it was an observation of the reality of "northern" economies.

These economies are currently depending on their immigrant workforce - from doctors and dustmen through to lawyers and bankers.

Trying to extract them would be like trying to extract half the DNA from a dual heritage child.