Austin Bay desribes his idea of a sensible approach to the possible threat of Iranian or North Korean nuclear missiles threatening the United States:

"What happens if Iran goes nuclear and puts a warhead on a missile? What can Japan, South Korea, and the US do if North Korea deploys nuclear-armed intermediate range missiles, or ICBMs? Sure– pray for success in political negotiations, and retain “offensive options” — slang for attacking the rogues’ nuclear sites. But a defensive capability is also very useful. We’re not talking Reagan-era Star Wars with hundreds of Soviet missiles arcing over the Pole. An Iranian or North Korea “missile pulse” would probably consist of six to twelve missiles (at the most). A “thin shield” anti-missile defensive system could handle this type of “limited” attack.

To do that, however, means increasing the range of inteceptors. According to Aerospace Daily and Defense Report, the [Terminal High Altitude Area Defense or] THAAD anti-missile program managers intend to explore increasing the missile’s range. THAAD is still very much in the developmental stage – it has a flight test scheduled for this fall."

My definition of "sensible" is probably a little different. It includes, among other things, some idea of how likely the potential threat is to become an actual threat (conceivable, eventually, in the case of North Korea; extremely unlikely in the case of Iran). It includes a requirement that the technology in question show some promise of actually doing what we want it to do -- promise shown outside a computer simulation. It includes some reckoning of how much more money the United States is going to have to borrow from the Communist Chinese central bank to pay for this project, and of the likelihood that this money will follow all the rest of the funds spent so far on missile defense in the last twenty years down the rathole.

In short: Do we need to do it? Are we able to do it? Can we afford to do it? In my book you don't have a "sensible" government program -- especially a multi-billion dollar program -- if the answer to each of these questions is "probably not."