Close to two years ago, a movie called "Don Jon," starring Joseph Gordon-Levitt, Scarlett Johansson, and Julianne Moore, hit theaters. Johansson, who plays Levitt's girlfriend in the movie, walks in on him one day as he's watching and masturbating to an adult film. That act alone caused the wheels of the relationship to fall off, and Levitt's character ends up finding a much more understanding partner in Moore, who doesn't seem to mind his habit as much.  The movie perfectly captures how some women may bristle at the thought or sight of their partners watching porn, while others may find it perfectly acceptable. The first group of women may contend that a guy needn't look at porn when he has a woman -- and a good one at that -- in his life. She may eventually sense that, because he finds pleasure in seeing other women naked, he must either be cheating or just isn't satisfied with her -- and, by extension, their sex life. Scarlett Johansson's...