[tropo]

One child is kind of a backup for another. If you can be honest with yourself, this becomes very clear once you have several kids of each gender.

Paranoia has risen because so few people have full-sized families these days. Losing one kid has become a tragedy.

[Declanomous]

On an evolutionary scale that's true, but on an interpersonal level it's less true. It's not like a person is more valuable because they are an only child.

[harryh]

As child mortality decreases people tend to have fewer children. This data point contradicts your assertion.

It makes people uncomfortable to think about people in economic terms(1) but that doesn't mean those uncomfortable people are right.

1. We see this in many areas of society from health care funding to liability laws.