[mikeash]

I think that's basically right. The worst crashes are usually frontal, and your entire body is evenly supported, rather than hanging on a seat belt or something.

Rear-facing seats are definitely not illegal in cars. Tesla has them as an option for a third row in the Model S. I think they would be legal in airplanes too, and the main reason they don't see more use is just that people are often uncomfortable not facing the direction they're going.