There's loads o' blame to go around. Parents bear much of the responsibility, part can't be helped because it's in the DNA. You look at the photographs/sepiatones of the women in my family back to my great-greats, and we are a zaftig bunch. Part can be affected by the parents, however, in educating their children as to healthy habits, supplying them with a healthy diet and encouraging active play and exercise.
Schools should help but they're falling down on the job. I applaud those who are changing their cafeterias and snack machines to offer healthy foods. Not all are. Also, physical education instructors bear a HUGE amount of blame when they fall into the habit of favoring the athletic few and shaming/humiliating those who need their attention and encouragement to be more active. Fast food places? Look - they're in it for a buck. They're being pressured to offer healthy alternatives now, and that pressure should be kept up...but anyone who thinks McDonalds is going to abandon those bland, calorie-heavy, nutrient-light basic burgers hopes in vain.
The media bears an immense part of the problem for encouraging a generalized and unrealistic (and often unhealthy) "ideal". They are abetted in this by the pharmaceutical companies, diet food programs (Nutrisystem, Jenny Craig, etc.), unscrupulous psychologists/counselors and doctors, cosmetic surgeons, and the fashion industry. I refer to this conglomerate as the "Low Self-Esteem Industry". There's billions of dollars to be made in making people feel inadequate. After all, if we were all healthy weight, active, well-adjusted emotionally and dressed to flatter our own body types, think how many people would be out of business...
I'm never gonna be rail-thin. I almost destroyed my health trying, and ironically ended up heavier than I started out. My solution? Stop "buying in". Make health the #1 priority. That means eating a diet that is balanced correctly for your metabolism, enjoying physical activity on a regular basis, getting plenty of water and rest, dressing to present YOU (not some magazine model), and above all...loving yourself enough to know that doing the above is good for you, makes you healthier and happier, and that this "ideal" being pushed on us all is meaningless. Ladies - if your healthy, best dress size is an 8, and some guy won't date you because he won't take anyone above a 6...forget him, and leave no trace of him in your memory. Anyone that superficial is too far down the intellectual food chain for your consideration. Trust me - you'll be a lot happier with someone who appreciates your healthy body, confidence and positive attitude.
We can affect ourselves, and we can affect our kids. Everyone else? That's a little dicier...but education and encouragement need to replace shame and ridicule. Trust me - this "old broad" has seen both the positive and the negative.