It’s a very bad idea. Here is why.
Today, North Korea released information to international agencies showing where it expects the first and second stages of “Unha-2”:http://www.totalwonkerr.net/1877/kwangmyongsong-kwangmyongsong-kwangmyongsong to fall. “Geoff Forden”:http://www.armscontrolwonk.com/2220/dprks-stay-clear-zones has a picture. The “International Civil Aviation Organization”:http://www.icao.int/icao/en/nr/2009/pio200902_e.pdf has a more elaborate version that includes civil air routes and other details. (See the second page of the PDF.)
What this shows us is a planned launch due east over Japan, dropping the first stage in the Sea of Japan, the second stage in the Pacific.
Currently, neither Japan or the United States has any known ability to shoot down a launch vehicle as it is boosting. There are plans, but the reality is still a way off, according to “MDA”:http://www.mda.mil/mdalink/html/mdalink.html. So if an intercept is attempted, it won’t be an intercept of Unha-2 (the rocket). It will be an intercept of Kwangmyongsong-2 (the satellite), once it has already passed over Japan, perhaps when it’s already in orbit.
In the past, the United States has maintained that its own satellites are equivalent to its sovereign territory. That’s a stance that’s difficult to maintain if one doesn’t honor it oneself. So entirely apart from the “legal issues”:http://www.armscontrolwonk.com/2214/shooting-down-dprks-satellite-launch-its-legal surrounding North Korean missile activities — and setting aside “how the NKs might react”:http://www.totalwonkerr.net/1897/shooting-down-north-koreas-launch — it would simply be making a very bad precedent for the U.S. to make an unprovoked attack on a foreign satellite, one that would undercut the security of the most space-dependent nation on Earth.
Let’s think about this a little before doing anything rash, OK, folks?