I heartily agree with you that the exclusion of any person due to race would be an appalling thing to bear witness to. I have been to that hideous bar on a number of occasions and the rotters that you speak of are generally without the social graces that even the most repugnant of scumbags are able to pull together, but based on the letter that follows your entry I have to admit that I am more compelled to believe the other side of the story.
This is not because I believe the losers who run that establishment to uphold any moral standard, but because they have worded their letter far more eloquently. So, what i am telling you is that if you have the desire to shout from the bell tower about an injustice, be sure to dot your 'i's' and cross your 't's'. And God help Korea if you are an English teacher; although, I am assuming you aren't .
Another thing worth mentioning is that there is very little evidence on either side that this was anything out of the ordinary in Korea. I'm not saying that you should accept intolerance or intolerable people, but; how long have you been in that country? Is it really your first encounter with such ridiculous behaviour? Are you not aware of the signs in bars that don't allow G.Is, or have you never been told to leave a juicy bar because you are white? One thing that is truly remarkable about Korea is that it tolerates intolerance like no other. I would say it's awful, but at the end of the day it's honest.
So, carry on with your boycott. If you can find something to believe in then most certainly you should continue, but don't count on it lasting for long. Don't forget about the silly bar down the street that shot the Irish men with rubber bullets (or so the story goes) and got its first waygook boycott. I imagine they are doing brisk business these days.
Good Luck.