THAAD seeking a hare in a hen's coop
Let's face it, in the wake of the Democratic People's Republic of Korea's fourth nuclear test and launching of a satellite, it is difficult to dissuade the Republic of Korea from taking measures to beef up its military for self-defense. But deployment of the Terminal High-Altitude Area Defense system is not a good option.
The THAAD is an anti-ballistic missile system of the United States Army designed to shoot down short, medium and intermediate ballistic missiles in their terminal phase using a hit-to-kill approach. The Korean Peninsula is only 1,100 kilometers long and Seoul only 40 km from the demilitarized zone. So most, if not all, of the DPRK's missiles targeting the ROK can only be short-range ballistic missiles with a maximum range of 1,000 km.
The threats from the DPRK to the ROK are not primarily the short-range missiles of the DPRK, just like the THAAD is not primarily designed, if at all, to shoot down missiles flying at low altitude. The missile threat from Pyongyang to Seoul essentially comes from KN-02, Hwasong-5 and Hwasong-6 with ranges from 160 km to 500 km.