The purpose of that THAAD ABM Missile System is to shoot down North Korean (or other enemy) inbound missiles. THAAD protects US and allied forces in South Korea and US navy ships.
If the US is stopped from completing the THAAD deployment we should withdraw our land forces from South Korea to some back-up position and let the South Koreans fend for themselves.
The world won't be safer with a few US nuclear guided submarines off the North Korean coast
