From the combox over at Dyspeptic Mutterings:
My eight-child family creates far less environmental impact per person then their ideal... Think for a second: under the OPT scheme, raising the same eight children would require four couples, four households, four sets of baby "stuff," four cars, four... you get the picture.
Large families are natural recyclers-- the crib we bought for #1 is still working perfectly well for #8. Most of the original baby clothes have been worn out at this point, but not quite all, and we certainly got more use out of them than the typical 2-child family.