It has a great deal more to do with selfishness than economic need.
How many 1 and 2 child families live in 4,000 SQ’ homes with two new cars and a pricy suburban address? Perhaps a used car and a third child might be better in the long run?
Selfishness is a point of view, economic reality is difficult to reconcile in this point of time relative to the society we have developed.
You can rationalize your point of view all you want, but what makes your point of view superior to that of those you wish to impose your beliefs upon?