have you ever met people that just wont stop pestering you even though you drop hints the size, and power, of mass weapons of destruction right in front of them? (no, i dont mean sales personnel that come knocking on your door)
and the fact is they dont seem to suffer from any bit of scorching or radiation or whatever nuclear weapons are supposed to do! i doubt they even realise the formation of the mushroom cloud.
in the end, everybody around them are suffering and they still continue to bug you like some irritating cockroach(no pun intended) that has resisted the whole bottle of baygon you've just wasted!
maybe the americans could take into consideration their great ability to withstand the destruction and do some scientific research to benefit the US and all other countries in defence against the north koreans.