You could very well be experiencing the correct emotion. Many people smile or laugh as a way to sort of self sooth / ease the intensity of the mood. Laughing can also be a sign of nervousness or discomfort. How do you actually feel inside when you're laughing at a sad situation? Also it could just be that you have become desensitized, with everything on tv and in the media in general truly sad things have been overexposed and developed now into a source of entertainment.