First, South Korea now has a conservative government after having a more liberal one for several years. Those individuals who supported the liberal government and its openings to the North are likely to see the conservative one as untrustworthy, just as happens here in the U.S. Polls show the young and better educated are more likely to be skeptical, I suspect they are also the more likely to be liberal.
Second, there is a fairly strong human tendency to decide that what we want to be true is in fact true. We see this among liberals in the U.S. and I suppose it is likely to be true among liberals in South Korea. They want relations between North and South Korea to be getting better, so they refuse to accept evidence that moves in the contrary direction, even when it is based in fact.
See this article in Bloomberg for details. I view South Korea's skeptics as being much like our "truthers" and "birthers" or folks who think the CIA, KGB or Mafia killed President Kennedy. That is, they are people who see conspiracies everywhere. Of course, on rare occasions the conspiracy nuts are right.
