Meeting in Geneva from July 30 until Aug. 17, the 71st UNCERD reviewed national reports on Costa Rica, New Zealand, Mozambique, Indonesia, and South Korea and released recommendations for them. On Aug. 9-10, it looked into reports submitted by the South Korean government. In the recommendations, UNCERD expressed discomfort about a prevalent notion in Korean culture of "pure-bloodedness," saying, "The whole concept came very close to ideas of racial superiority."
This is, of course, one of these stupid old ideas created for nationalist purposes that people in Korea carry on without thinking about whether or not they make any sense. While many Koreans do believe this to be true, most of the smart people I know know it to be ridiculous, and I have often heard the opposite "Korea is a rich purée of other groups that has simply had the lumps blended out" view, citing ancient immigrantion from countries as far afield as India and Vietnam, and of course Mongolia, whence Korean babies are said to get their famed 'Mongol spot'.
Which many Koreans will tell you only occurs in Mongolians and their close cousins, the Koreans, although this is patently false.
Anyway, yeah, can the pure-bloodedness fairytale, Korea.
Update: The Marmot has a detailed breakdown of exactly the information I have heard about immigrants throughout Korea's history