Questions you'd prefer not to answer

Here's something to worry about:

The Arrow is the successor to the American Patriot missile system used to shoot down Saddam's Scuds during the 1991 Gulf War. But where the Patriot attacks the incoming missile as it nears its target, the Arrow is designed to intercept a hostile missile much earlier, in the upper atmosphere.

From Israel's perspective this is a crucial advance, especially if the Iranians were to attempt to fire missiles armed with nuclear warheads. "There's no point shooting down a nuclear missile once it's over Israel - the devastation would be just the same," an Israeli military officer explained this week. "The idea is to take it out long before it hits Israel."

That would mean such a missile exploding somewhere over Iraq or Jordan, thereby potentially causing widespread devastation in those countries.

It's not a case of 'innocent shields' exactly, but it raises similar issues. To save its cities, its people, may one country defend itself by transferring the potential cost of an attack by a second country to third and fourth countries? Does the second country bear the full responsibility for what happens by obliging the first one to defend itself in this way, because there is no other technically feasible method of shielding its population? Or is the responsibility for the devastation in the third and fourth countries shared by the first and second countries?