By this argument, we should do absolutely nothing to prepare for dirty bombs, chemical assaults, and any terrorist attack other than plane hijackings.
Yet we can spend $300 billion fighting the oil war while ignoring Al Quaeda. And we can pretend that we are chasing 9/11 terrorists, until that lie crumbles. Then we can pretend that we are stopping a tyrant that poses a risk to us, until that lie crumbles. Then we can pretend that we are building democracy (a damned fool stupid thing to do), until that lie crumbles.
But the message you want to send to the American people is that it doesn't make sense to prepare for likely disasters until after they happen. Nice.
If we truly can't afford it, we have to admit it to ourselves. Fine. But we also have to stop burning money on idiotic shit like the Iraq war and giving subsidies to people who buy SUVs over 6,000 lb (yes we still do this inane crap).