As the number of obese and morbidly obese persons begin to rise and the United States of America even have to create a new category called SUPER morbidly obese for those people who weigh in the vicinity of a TON (that's as heavy as a small car!) you have to wonder, does the government have a roll to play?
While we all like to think we're in charge of our on destinies, our past influences our decisions far more then we'd like to think. If for example you grew up in a household where it was junk food every night and sports weren't encouraged, then guess what you're likely to be like as an adult? Even more so, guess what you're likely to be like as a parent? 
I do agree that the individual needs to make their own decisive changes in their life. Over weight and obese people need to exercise, with an active lifestyle. If you feel self conscious about exercising in public or like Sarah you have in your head that walking places is "scummy" (which of course it isn't, I walk a lot and I'm certainly not scummy) then you could always buy a treadmill or other at home exercise equipment until you feel more self confident. The families of Morbidly and super morbidly obese people; people who can't even get out of bed due to their shear weight; need to stop enabling their food habits. If you can't get out of bed then you'll eat what you're given. People need to get up and move around, they NEED to exercise, daily and develop an active lifestyle so that exercise becomes a part of every day things instead of a chore they have to schedule in separate to everything else.
But I also think government has a role to play. It is clear at this point people are NOT going to change on their own, they need a good hard kick in the right direction which is where government comes in. There are several measures governments in the western world need to take.
(1) P.E. before school for pre-school, primary school and high school students. That used to be a part of schooling in the 70s and it worked well. Governments cut it to free up money, but it was actually a very valuable tool. Not only will it mean every child exercises daily, but it means they will be able to concentrate better in school, be more confident and are far more likely to carry on the approach into adulthood.
(2) The development of more Parks and sporting fields. There are some areas where there is a distinct lack of these sorts of facilities and without them people are unable to include certain activities in their lifestyle which would aide in the weight-loss problem. Sports are a major part of combating obesity, so without a facility to hold sporting events people can't expect to be healthy for very long.
(3) Proper dietary and exercise education. For far to long people have been going on about diet. About cutting foods out and limiting calories. This is a MAJOR factor in why we have the obesity problem the western world is facing today. Our bodies have evolved in a way that requires us to move around and use energy. But our society has evolved in such a way that we don't really move around and use energy anymore. This is the BIGGEST systematic problem of all and the REAL cause for the obesity problem.
You can attempt to blame fast food all you like, but the fact of the matter is the average diet in the 50s contained FAR more calories and FAR more cholesterol then we consume today. Our lack of movement is the huge problem. Food isn't the enemy it has been made out to be, it's simply food. ALL food is perfectly find in MODERATION. Too much of anything even carrots will cause you problems. In this way government should educate at the primary school, high school and adult levels about the importance of MODERATION and ACTIVE LIFESTYLE.
(4) Legislation making it a crime for gyms and weight loss services to give INCORRECT information on weight loss or to misrepresent the facts should be brought forward. It should be a crime for a weight loss service to continue the lie that it's all about diet and you need to cut out foods and calories.
(5) Cooking classes should be reintroduced to schools. One of the biggest reasons fast food has become so popular is people have lost the skill of home cooking. If we teach it to our children in a proper way they are more likely to make good food choices.
(6) Amendments to the child protection laws to include obesity. Children can only become obese through ineffective and neglectful parenting. If you are teaching your child the correct eating and exercise habits then there is no possible way you child can become obese.
(7) Legislating more strongly about the advertising of food. NO FOOD products of ANY kind should be advertised during children's television viewing times for example. Children shouldn't be in the drivers seat, that's the parents job, therefore children shouldn't be advertised to.
(8) Parenting classes, perhaps mandatory, for people with new babies. These classes would address general issues like diet and exercise, conflict negotiation, basic first aide, child development, looking at things through your kids eyes on their level and ideas about games that can be played with your child at different stages of development.
(9) The banning of gastric bypass surgery. It doesn't do anyone any good in the long run and is bound to have some undesirable long term side effects.