How?
Let's try a little simpler...
How about we let the airlines themselves provide the amount of security they feel is appropriate. Then, the passengers can determine the amount of screening they are willing to accept before they make the purchase of the ticket to fly.
In this fashion, the airline and the passenger determine the level of risk each of them are willing to accept. If too many passengers determine the level is too lax or too strict, for the most part, only the airline suffers until they change their methods or another carrier provides an acceptable level. In short order (barring collusion), the free market would determine the amount of screening that is acceptable to the general public / frequent fliers.