[hugh_]

Without any suggested strategy that would defend against all possible attacks, though, it's not much of a suggestion. The current strategy may be the best one available. If unreliable two-component powder+syringe underpants bombs are the best option currently available to potential aircraft bombers, then that's definitely something.

[_cbsz]

The point is that the cost of defending against all possible attacks may very well be too high to be worthwhile. If you argue that this is impossible, consider the extreme case where the cost is equal to our GDP (or an appreciable fraction thereof).