You should absolutely blame the Diet Coke and the execs that push it. Almost every aspect of eating the food we need to live is distorted by people trying to make as much money as possible at the expense of our health. They know it. They spend billions doing it. You likely wouldn't have been consuming it or so much of it if it wasn't on every billboard and commercial and was at the back of the store in plain boxes without the big 'sale' or 'bogof' stickers. It doesn't have to be this way and you shouldn't blame yourself or any other individual for a social problem.