Car seat legislation as public policy contraception

I am an enthusiastic empiricist and rationalist, focus my management consulting career on effective decision-making and am always providing clients with examples of unintended consequences arising from naive decision-making.  

But even with that background, I did not see this one coming.  Haven't reviewed the methodology and the effect size might be too large.  But my goodness.  What consequential issues of life and death and such an unexpected outcome from such well-intended legislation.

From Car Seats as Contraception by Jordan Nickerson and David H. Solomon.  From the Abstract.

Since 1977, U.S. states have passed laws steadily raising the age for which a child must ride in a car safety seat. These laws significantly raise the cost of having a third child, as many regular-sized cars cannot fit three child seats in the back. Using census data and state-year variation in laws, we estimate that when women have two children of ages requiring mandated car seats, they have a lower annual probability of giving birth by 0.73 percentage points. Consistent with a causal channel, this effect is limited to third child births, is concentrated in households with access to a car, and is larger when a male is present (when both front seats are likely to be occupied). We estimate that these laws prevented only 57 car crash fatalities of children nationwide in 2017. Simultaneously, they led to a permanent reduction of approximately 8,000 births in the same year, and 145,000 fewer births since 1980, with 90% of this decline being since 2000.

In saving 60 lives, we preclude 8,000.  That doesn't sound like a policy we should support.  If the maths holds up.