I know this story is a bit out of date now, but as I recover from the usual New Year hangover I just felt the need to throw in a few thoughts on the subject.
Back at the beginning of December a number of Korean celebrities got together and held a news conference to call for South Korea's harsh laws on cannabis to be relaxed (OhMyNews article). This opened up a bit of debate on the subject in an environment where previously drugs=evil had been the prevailing idea.
The Korean socialist newspaper Ta Hamkke (다함께) provided a good overview of current knowledge about the effects of cannabis smoking and some good comparisons of the harm caused by alcohol and cigarettes. (Dependency on nicotine is apparently 6 times stronger than cannabis and alcohol 4 times stronger).
Obviously you can rehearse various arguments about individual freedoms versus the right of the state to intervene to prevent people form harming themselves or those around them. But to be honest I think these arguments often miss the point. We really have to ask why it is that governments find it convenient to ban some substances and not others, often regardless of scientific evidence about their relative harmfulness. Obviously there must be historical reasons for these idiosyncratic laws, but personally I think that the prohibition of drugs also has a lot to do with social control. Of course is would be foolish to argue that drugs are some sort of revolutionary force that can change society, but they are often associated with the sorts of things that governments are afraid of - youth culture, artistic expression (especially with a political edge) and sexual freedom.
Not only this but prohibition also gives governments a good excuse to clamp down on people who say things it doesn't like. It can also act as an ideological bogeyman to create a backlash against a wider sense of political and social change in society or to pin the blame for social problems on the 'decline' of youth or often on 'foreign' influences. This was the case in Britain in the 60s when various musicians were charged with possession, and right up to the present day (despite the recent relaxation of laws) suspicion of possession has been used as the perfect all-purpose excuse for stopping and searching people (with a heavy bias toward the young and ethnic minorities).
In Korea the use of cannabis is not particularly widespread, and like Britain in the 60s it is artists and entertainers who have borne the brunt of prohibition and who are used as examples to the rest of society. I know of one or two people through personal experience who have been on the receiving end of this treatment, including one quite famous and venerable old traditional musician who should be celebrated by the goverment rather than thrown in prison for having had the odd reefer. Handing out prison sentences for the possession of tiny amounts of marijuana seems irrational in the extreme. Hopefully the new debate on this subject is a sign that another remnant of the old days of authoritarian rule might be on its way out. I have a feeling though, that the ideological and control value of cannabis prohibition is still too important for the establishment in Korea.
On a historical note, I often wonder how much marijuana was used in Korea in premodern times. Hemp has been one of the basic fibre plants used by the common people to make clothing for hundreds, if not thousands of years. Since it is known that cannabis (particularly hemp seeds) was long used in Chinese medicine it seems likely that it was also used for medicinal (if not recreational) purposes in Korea too. Evidence on this is probably rather hard to come by, but
this site does give some interesting hints on the historical use of cannabis in Japan. To this day large fields of hemp grown to make cloth can be found around South Korea. I remember seeing a documentary once about the growing problem of people raiding farmers' hemp fields at night. Typically for Korea all the farmers in the programme were rather old and seemed completely perplexed by the idea that people would come and steal their plants so that they could smoke them.