Bryan Caplan's "Selfish Reasons to Have More Kids" is the antidote to Amy Chua's best seller, "Battle Hymn of the Tiger Mother." Whereas Ms. Chua insists that parents should have few children and then drive them relentlessly toward perfection, Mr. Caplan argues that people should have more children; that they are cheaper than we think; that parenting is less important than we imagine; and that kids can basically raise themselves.