There is no magic dirt. The Koreans will learn this good and hard.
I suspect the reason why the Koreans are willing to consider mass immigration is because, deep down, they really don't like themselves. Korea is a relatively small country compared to Japan and especially China. China dominated Korea for 400 year, which is why all Korean names (such as Park or Lee) come from China. Japan, by being an island country, has had a "nice" history, with the "kamikaze" typhoon destroying Khan's fleets when they tried to invade Japan about 700 years ago. This is the only time, prior to their defeat in WW2, that Japan was ever threatened with foreign invasion. Korea, on the other hand, was invaded and added to the Khanate. In short, the Koreans have an inferiority complex compared to the Chinese and Japanese. This is why they are willing to countenance mass immigration.