The things is what you are talking about is priority, but what I am talking about is financial feasibility
Okay, let's imagine a fictitious scenario, let's say there is a Patriot Missile system protecting the White House. And there is an armed drone intruding an airspace of the White House. Now, it's imperative to shoot down the drone because it can do damage to White House or the President of the United States. Let's assume the interception rate is 1 : 1
Now, let's expand on the issue, on one side, you have 100 patriot missile system, and on the other, you have 100 armed drone, Now, would it become the same situation to shoot down the 100 drone using 100 Patriot system? Now, if we put in different variable, what if US only have 200 set of Patriot Missile? Now, you are in a cross road.
Scenario 1 : Shoot down all the armed drone using all 100 Patriot Missile system. However, doing so, you will half the whole number of Patriot System available to use to protect all other part of the country.
Scenario 2 : Do not use all the missile to shoot down some incoming drone, let White House take some hits. Say you shoot down 50 of those and let the other 50 go pass. You still have 3/4 of the stock protecting the rest of the country.
Scenario 3 : DO not shoot down any drone at all. So you can use the maximum number of missile system to protect the rest of the country.
Now, here's are the kicker, given a Patriot Missile Battery cost 3 times as much as a Tomahawk Missile, and 6 times as much as a Russian Missile, and 10 times as much as an unarmed Chinese Drone. For the price of 1 missile your enemy can make 3 cruise missile, 6 Russian missile or 10 Chinese Drone. So now the equation is once again changed. You have 200 patriot missile system protecting all of US. And your enemy have, let's just half the rate, shall we? 300 Tomahawk Missile or 600 Russian RD-55 Missile or 1000 Chinese drone. We all know one missile can at most intercept 1 Tomahawk Missile, 1 RD-55 Cruise Missile or 1 Chinese Drone. Now, is it financial possible to intercept all target? Hence is it financially feasible to intercept all the target?