It isn't a question of desire. If the economy of the north collapses and millions of people are on the verge of famine, the south needs a plan to maintain some sort of order.
Honestly, I don't have any right to say one way or the other is right because I'm not even Korean, I just think that we in the west need to stop taking as a hypothesis that if NK collapses that it is SK's responsibility. I think it is up to the South Koreans to decide whether they want that, and not us [1].
[1] And yes, that's what this article is about, the government is preparing for this contingency, but as we in the west know, our government doesn't always do what we want.