This assessment works because in the Cold War, the goal isn't to intercept enemy missiles, it's to prevent your cities and civilization from being destroyed or being overly coerced - which is something that you could achieve much cheaper via mutual deterrence.

Once you can no longer achieve mutual deterrence (perhaps because you are a nation who has a streak/role of engaging in interventionist wars of choice, or maybe you are planning for the case when deterrence fails, and you are now under attack), you have to decide how to protect your assets, if even in a limited way.

An airbase which gets overwhelmed and lost after 5 days of bombardment is an airbase that hopefully was able to contribute 5 days of value to your effort. It's true that the costs will not always work out in your favor.