Maybe you can redefine the topics you treat in the course to include additional material that isn't so depressing. You be da boss and get to call all da shots. This might also be a topic in and of itself for exploration in the course: the impact of this material on regular consumers of this stuff. If its effecting you, I'm sure it is effecting your students. They are not all hardened sociopaths. And it is not just movies--look at how many violent and sexually explicit video games are on the market and enthusiastically embraced by a segment of the population. To keep dealing with this topic on a daily basis, you may need to develop additional critical distance. Or maybe it is time for you to develop a course on a different topic and offer it once and a while, to break things up.