While in S. Korea I was on a hilltop just outside Osan AB with our radio when some S. Korean students came to protest our "presence". I never felt threatened in anyway. After about 30 minutes or so they stopped chanting and sat down. We went over and talked with the ones who spoke English. We ended up swapping smokes, gave them some chocolate bars, and talked for a little while. We shook hands as they left.
The older Koreans don't protest. They know why the US is there.