How do we know whether they were “allowed” to defect, and in fact, may be spies for the NORKS?
That’s always a possibility.
How do we know whether they were “allowed” to defect, and in fact, may be already infected with some of Fatboy Kim’s bioweapons?
They do infiltrate spies, all the time, but without anyone knowing. It's a long coastline, and a small boat dispatched from a submarine is hard to spot.