Airbags were mandated because not enough people wore seatbelts.
I'm not saying airbags are worthless, they're not - they work, but is the reduced injury in most cases worth the cost? I don't know - when worn with a Seat Belt, Airbags don't generally save lives, but they reduce injury level - the core issue is, we pass regulations with the idea that everything we do ought to be perfectly safe.
A good example is backup cameras, a backup camera adds somewhere between 250 and 1000 dollars of cost to a car, yet only about 200 people or so a year are killed in such a way that they might have been prevented by backup cameras. We sell 17 million cars a year or so every year, which means, the added cost of backup cameras is somewhere between 4.25 and 17 million dollars a year - meaning assuming the regulation 100% effective, we spend 21,250 to 85,000 dollars per death prevented - most of which could be prevented if the operator of the vehicle just did a walk around before pulling out of a parking space. Is that 17 million a year well spent? Airbags lead to a similar set of questions, is the cost injuries prevented enough to offset the cost of the airbags?
I don't know, I would suggest we should be asking these questions, rather than just scream 'for the children' and put another rule in place - because in the end all of these rules add a cumulative cost - and the poor pay it first. Bear in mind, I'm not suggesting we get rid of all emissions and safety standards for everything, I'd just like some more choices in what I find acceptable for my personal risk level - I, for example, might not buy a car with 16 airbags or however many you can get now - I might chose to only buy an option with two airbags, or none at all (one of my cars is without airbags). Similarly I might chose a backup camera as an option, because it will save me body damage when backing in or out of parking spaces - but I should still get that choice.