Today's (American) society is increasingly fragmented. Add in tendencies toward individualism, plus sheer numbers (with 300 million+ , what's a few people without kids), and I can see why some people feel having kids is a choice, not a duty.

I agree that having kids both costs and benefits society, but when every man feels himself to be an island that's a hard sell to those without kids, who feel increasingly alienated.

This is a nice freedom, by the way, for those who want it; you can opt out of the stroller brigade & feel that society will keep humming along anyway. I hate to think of the external or internal pressures that would have to arise for this freedom to evaporate!