Forty or fifty years ago the size of families tended to be a little larger. Sure, there was less birth control, but people also seemed to want to have more kids than they want today. Smaller families are a luxury good, like clean water and air.
Half a century ago futurists dreamed of agricultural methods that would produce huge vegetables, genetically modified, on minimal land capable of feeding multitudes. Today we eschew genetically modified foods, etc. in favor of organic foods, even when we have no naging reason for doing so. Organic foods, are indeed a luxury good, just check their prices.