Jessica Alba is pretty. Like many actors and actresses, her attractiveness has helped propel her stardom, but her pleasing physical features have brought with it a definite downside: People assume she’s dumb. When the most memorable moment in your film career, arguably, is asemi-raunchy dance in “Sin City,” it’s hard to combat that perception, but Alba sure didn’t help herself with a somewhat-innocuous comment she made recently that has every screenwriter in town gunning for her.