I think this will help some but not all. Some don't eat fast food, so it won't help them. Some people are borderline heavier or need to lose 30lbs or less, this category I think would be helped the most. They are already somewhat calorie conscience and that little extra info/boost may keep them from becoming obese. Those that are morbidly obese already, unless it's a health issue, are in a habit of eating unhealthy, have a pattern and a way of thinking that I am not sure this is enough to help them. Maybe, maybe it will. I would hope so.
As for obesity in children, I think it should be considered abuse.
My sister in law and her husband are obese and their 2 kids are obese, morbidly obese. It makes me VERY sad to see 2 kids who can't play, can't move, can't run, can't fit in the front seat of my car (YES Seriously). I think it's abusive to allow your child to get that large when it's caused by eating. There are instances when the child will eat really bad outside the home, but the parents should teach nutrition in the home, eat well in the home and not have sugary, fattening snacks in the home. That will help their calorie intake while home immensely.
People who say "we should be in control of our own food decisions" I think is a cop out. The nation has an obesity epidemic. We WERE in control and look what we did to ourselves. Now our health care has SKYROCKETED in price, the #1 killer is heart disease, which is a direct correlation to eating poorly. The fed is trying to control those who cannot control themselves. The choices are not taken away from you, but NO ONE NEEDS a 32oz SODA. NO ONE. I don't care how thirsty you are. 16oz of soda is plenty, switch to water if you are really thirsty or yes, buy a 2nd soda. I think they are hoping most people won't dish out the money for a 2nd soda, which in turn helps the person more than ANYONE else. No one stands to gain from this except the people. The only way money is made is if people continue to make the poor choice and do buy 2 sodas, or do get the worse menu choice.
Just like smoking. Its a health risk but people who are not smokers are ok to TAX the smokers up the wazoo.... yes, they can pay it and keep smoking. The choice is not taken away from them. It just is going to cost them more to continue. So why not the same for poor food choices? There are menu items that are the same price or cheaper that are healthier choices for those w/o with little money.
I know it's a bigger picture than this, I know it feels that another freedom is being taken from the people of the 'free world' .... I wish that it didn't need to be this way, but we (as a collective whole) have opinions on what is right or wrong for the gov to take away or regulate, like gun control, cigarettes, certain drugs, alcohol, driving age, etc... but honestly they are all the same, food is up there as the same thing.