Shot exchange is indeed a problem, but it's far more complex than this makes it sound. The opportunity cost of _not_ shooting down the drone isn't the cost of the drone, it's the cost of whatever it's going to destroy if you don't shoot it down.

Sometimes it makes sense to use a million dollar missile to destroy a $5,000 drone, if that drone would otherwise destroy an even more expensive air defense radar or energy production facility. This says nothing about the cost and value of the lives that might be lost in an enemy strike.

We would not be safer if the enemy had cheap drones and we had no weapons capable of fighting back.

The main problem is that air defense interception is incredibly challenging and expensive primarily because a mid-course defensive interceptor needs considerably greater capabilities than the weapon it is intercepting, because it needs to catch up to the incoming missile or drone mid-flight.

Sure, this can lead to massive overkill problems. Yes, the US should invest more in the low end of the high/low mix. But no, this does not mean there's no place for the high end, or that they should never be used to destroy lower end targets if that's all that is available.

A more interesting challenge, if you ask me, is in the naval domain. Imagine a capital ship has two options for defending against incoming threats - either fire an expensive and limited stock interceptor missile with a 99% kill chance, or wait until the threat is inside the range of a cheap cannon or laser system with a 95% kill chance. There's a real command level tradeoff to be made here. If you shoot every drone with interceptors, you lose shot exchange badly, and you just run out of interceptors. But if you let every target through into the engagement range of your close range systems, you run the risk that one makes it through to your ship, potentially causing damage and casualties.

The future of war is going to be wild one way or the other.