(This is my own opinion only)
Although I am not Korean, acting as a global citizen, I would choose "for" rather than "against" towards the Korean unification, in terms of economic and social dimensions. (Owing to my lack of knowledge on Korean politics, I neglect to write the political part thoroughly.)
Politically, what i reckon on the surface of the unification: the rise of Korean international status due to the whole nations look more complete and the institution of Korean government would be more stable and more diverse.
Economically, the unification of Korea would be prosperity for the economy, not only to herself but also to the whole world. The idea of communism can help Korea build its economy with some plans while that of capitalism can help her to build up its market economy.Taking Germany as an example, before 1989, Germany was divided into two parts--West and East. If you are history students, you will realize East part is communist and West part is capitalist. There was ideological difference between two nations. Until 1 year after the fall-down of Berlin Wall in 1989, East and West Germany was reunified into one nation. Nowadays, Germany is one of the richest countries in the Europe while European countries such as Greece, Spain, Italy, Portugal and Iceland(we call them "Piigs"(歐豬五國))Besides, even some magazines drew cartoons (below), saying that world economy requires Mrs Merkel, Premier of German Government. It shows that Germany has played a significant role in the world, in terms of economy. Therefore, there would be probably a boom for the Korean economy as well as an advantage towards the global economy if the reunification of Korea exists in the world, with reference to the German economic development. (She would be second "Germany" and an imaginary enemy of China.)
Yet, the unification might be a problem to the North citizens or South citizens. Some of the South citizens might have more hatred on the North ones. The relationship between Hongkongsters and Chinese is a very typical example. After takeover of Hong Kong in 1997, there was a "moral panic" in Hong Kong against the return to China---the influx of emigrant. Hongkongsters fear about the spread of Chinese communism and they did not want to live under the institution of "one-party dictatorship", so they move to foreign countries. Nowadays, Hongkongsters hate mainland Chinese very much since those chinese has lower educational level and their actions ruin the image of Hong Kong, as well as those Chinese are impolite and pride, they love going to Hong Kong to buy the milk powder, to give birth their babies(main purpose: their children can enjoy 12-year free education), thereby serious social problems such as inflation and hardships in Hong Kong. South Korea might suffer from the situation like Hong Kong after the unification. However, Hong Kong is a very small part of China and the influx of mainland Chinese to Hong Kong such as buying stuff and giving birth as well as the academic degrees, is serious problem towards Hong Kong because she is very small nations while mainland China is very big nation (relating to geography). But South Korea and North Korea are half-to-half. Half of the Korea is South and another half is North. The situation of Hong Kong might not be found in South Korea due to the geographical difference.
Negative impact in terms of political aspect: more diverse in institution=>more struggles in the Congress, and make the policy difficult to pass, as well as the rise of meeting adjourns(流會).Take Germany and Italy in the 1930s as an example)
In conclusion, what i am thinking is, the unification of Korea benefits South Korea economically while it has a positive impact in terms of society towards North Korea. But there is also negative impact of the unification of Korea. The unification of Korea not only based on what North and South citizens think, but also their leaders. If most of them think that the unification sounds great, the leader agree that the unification can help to build up the economy, the institution as well as society, I believe that the unification is possible and there will be less negative influence to the South and North ones. But it depends on what the two leaders think. Therefore, to a large extent, I think Korea's unification is considered as "for" rather than "against" towards both South and North Korea.
In the recent year, the new leader of North Korea, try to be like Deng Xiaoping in China---to open up and reform the North Korea. After the opening up, the unification seems possible to Korea. However, the "nuclear crisis"(remember the nuclear weapon?) of North Korea is still in alarm. On the other hands, the ones in South(see those celebrities and university students), want their countries to unify with North Korea so much. Korea seems possibly unified.
As a Chinese, if I was working as the standing committee in the Politburo, i really did not want them to unify. I would be scared after the unification: Oh my, other than Japanese, i have another competitive opponent.