Stick to your guns. Watching English language movies with Korean subtitles most probably retards their ability to speak, listen to, read, and comprehend English. Young children will sit through the movie grooving on the colors, if nothing else, and pick up some components of the language. Older children can be more feisty. Since it's a discipline issue, there are a myriad of ways to handle it: You could pause the movie and ask the student talking to stand up, and read the English language subtitle on the screen, each time, until they tire of having the movie paused.
If the other teachers complain, you might ask them to explain to the students that roughly 40% of what they read in a subtitle is a mistranslation, and that if they can learn to watch movies in English, their comprehension will improve, etc., etc., blah, blah, blah . . . or . . . **** [MOD EDIT: be quiet].
English subtitles seem essential(you can download the subs for most films) and it might help to give the students a choice of which movie to see, showing them the film trailers to inform their choices.
I was showing a film to an English club today and one of the teachers came in and started translating bits of the film into Korean. I took her aside and told her I could get the Korean subtitles for the film. "Oh, could you?" she enthused. Yes, but this is an English club. Sigh. "But they can't understand . . . " Of course, they can't understand everything, but we can't either / / there's too much information on the screen. So we selectively perceive. For foreign language learners, staying outside of their Mother tongue for longer than a few minutes can be a challenge, so some students are simply learning that when they sit quietly and let an English language movie wash over them. Any yammering in Korean, or subtitles, would destroy it as a learning Experience.
Unfortunately, few movies will satisfy everyone, and students accustomed to being the center of attention may be disruptive at the slightest discomfort. I have found that having new movies is a plus. Optimally, class time spent viewing movies is a very legitimate exercise if it teaches the students to spend part of their entertainment time in the target language instead of Korean: This will reduce their study time, so it's a win-win.
If they insist on being disruptive, you might move to singing, which is also legitimate. There are some PPTs to songs on this site, and many of the vids on Youtube have lyrics on screen: The World cup "Waving Flag" one is popular at the moment. Be forewarned: Someone has invented Korean lyrics for the tune, so if some AH starts shouting that during the lesson, you might have to switch to another song if he doesn't pipe down. You can shut off the sound and rehearse the lyrics with the video's graphics prior to playing the tune.