well...the thread was a sort of humerous one, DtG...but since you asked...

" How come ordinary people with big families seem to be fair game?"

well...I dunno about 'fair game', but this world is getting to the point where having a big family "just because you want to" can no longer be defended. Granted, changing the habits of thousands of years will be hard, but there are just too many people!
The world population is over 6 billion, and ¼ or more of them are in poverty and hungry and lacking space and a decent life. The earth passed the amount it could support 'indefinitely' about 1950...

It all means that if you have 5-6 or more, someone has to have none to compensate. The Chinese have been trying, but don't have much success in rural areas because of a 'tradition' of large families. Now the Chinese economy is becoming a real drain on the rest of the world as all those people try to raise their living standards.