"Coldly logical, and depressing in its inevitable conclusion. I hope the author is wrong."

I don't find it logical.

First sentence:
"Modern armed forces continue to be structured for large-scale war, but advanced societies whose small families lack expendable children have a very low tolerance for casualties."

First of all, parents, don't find any of their children "expendable" regardless of number in the family.
And if one is instead looking broad demographics, it also is illogical- we have a relatively a small military because of economic factors, not from shortage of warm bodies.

And more America parents are losing their children to car crashes then any loses from any war in modern times.
And as a guess, in significant percent of car accidents, the parents bought them the car- though it's probably a safer thing to do, then giving them a bicycle instead.

"On an average, there are more than 6 million car accidents on the roads of the US, annually.

More than 3 million people get injured due to car accidents, with more than 2 million of these injuries being permanent.

There are in excess of 40,000 deaths due to car accidents every year. Although this is a very high number by itself, some heart can be taken in the fact that statistics show that car accident fatalities have been witnessing a downward trend in recent years.
....
For those in the age group of 1 to 30 years, the leading cause of death is due to being involved in a car accident. People, who are between 15 to 24 years, and those who are above 75 years of age, are the people who are most severely affected by car accidents."

And if we all riding horses, it would then be horse accidents.