Well, true, the chances are VERY remote of a carseat making the difference between life and death, or even being fine and being injured on an airplane.
Same is true of adult lapbelts... even moreso. Yet, I'm required to wear my seatbelt. The plane won't take off until they've walked down the aisle and made sure that everyone has their belt buckled.
Why would I go with a *lower* standard for my child's safety?
As a family, we don't fly unless we can afford a seat for everyone. We bring carseats. It's much more comfortable; even if you're holding your baby most of the time, having somewhere secure to put them down for a minute while you stretch your legs or drink your tea is really, really nice. Kids who are in a familiar seat will often cope better with an unfamiliar situation, and if they're the type to sleep in the car, they'll do it on the plane, too.
The only reason it's allowed to have under-2's on a plane without a seat is because the FTA crunched the numbers, and decided that the price difference would push enough families into driving instead of flying that the injuries from car accidents would be greater than the harm that could come to lap children. It's not "safe," it's just safer than driving... but then again, a LOT is safer than driving! ;-)
Ultimately, if we were the one in a [number with lots of zeroes after] flight where it *would* make a difference, could I ever live with myself for having decided my child's life wasn't worth $XXX? Me, no, I'd never recover from that. There may be others who can make peace with that decision in the same situation, and I don't fault them for it, but it's a level of serenity and trust in the universe that I simply don't have.