I am 100% in favor of mandatory nutrition information at the point of purchase for ready to eat foods at all places where they can be purchased (e.g., restaurant, vending machine, movie theater, bowling alley). I believe that an interpretive system, like the multiple traffic light (red for high in a nutrient, amber for moderate and green for low), is crucial, but I understand that nutrition labeling as a means to change behavior will always be less effective than other strategies, like zoning laws and taxes.
The provision of nutrition information, even with a color code or star rating system, leaves individuals free to make an informed choice. Unfortunately, choosing food isn't the same as choosing a dishwasher (which also comes with content info and a rating system).
There are many things that influence a food choice. One of my favorite theories or frames which addresses these nuances is behavioral economics.
READ THIS GREAT ARTICLE, by Liu, Wisdom, Roberto, and Liu (2013).
The reason I think the traffic light labels are crucial is two fold. First, most people do not have awareness of dietary guidelines or the nutrition knowledge that allows them to determine if a food is high or low in items that are best limited (e.g., saturated fat, sugar, salt, calories). Second, many people are present biased in their (food) decision making. In other words, the desire for the taste or the happy memory associated with a certain food, is first and foremost in a present biased persons mind. The needs of 'here and now' trump any consequences (weight gain, ill health) that might occur sometime in the future.
There is another factor (noted in the article I linked earlier) that I wanted to share. I think you will go "oh my gosh, that is so true!" just like I did. This is the belief or confidence we have in the self-control of our future selves. For example, on a certain day of the week, you know that you should skip dessert. You are full and can't afford the extra calories. But it is someone's birthday so you just have to have some, and you'll do better next time or the next day. Then someone brings cookies to the office and you really shouldn't have any, but everyone else is having them, and they really taste good, so you eat the cookies and promise yourself that tomorrow you will have dinner with out bread. Oh, but tomorrow comes and the waitress served bread so you have to eat it, right? etc.....