"That would crash house prices as drasticallycutting migrants...

"That would crash house prices as drastically
cutting migrants would reduce tenants and
home-buyers. Markets would plunge."

Good, the property market needs a good correction, currently it is unsustainable. It is one of the factors leading to Australia's overall uncompetitiveness, as property values feed into wages.

"Drastically cutting migrants would cut retail
sales. Retailer share values would plunge."

Babies require much more retail spending that migrants, also a cheaper property market would lead to cheaper commercial rents which would help retailers/

"To shut the gate on migrants and refugees
is to shut the gate on Australia's prosperity."

Not if we have an adequate birth rate.

"Besides, who would do Australia's Dirty Work
of cleaning pub toilets and emptying nursing
home and hospital bed-pans and slaughtering
bullocks: graduates from Melbourne Grammar?"

Only migrants are suitable for this line of work? Or is welfare too generous, allowing people to become too picky?