Even blaming parents is a gross oversimplification. I was adopted as an infant and became the first and only person in my adoptive family to be obese or even overweight as a child. My parents did everything they could to try to help. They weren't highly educated, money was tight, and they made mistakes, but they did their best with what they knew and were told by my pediatritian.
Once, at the grocery store, a stranger stormed up to my mother and started yelling at her, ranting about how my mother should be ashamed of the way she was neglecting and "starving" my skinny baby brother and overfeeding me and that she should be feeding my brother instead of me.
I started crying because I was terrified that my mother would listen to the angry lady and would stop feeding me. I was already at 5 on a strict diet and was HUNGRY all of the time. My parents were always trying to get my brother to eat more (and more sugary and fatty "treat" foods) and me to eat less. We both had a treat jar at home (ceramic canisters, and I got the smallest one). My brother could have one a day and two on Saturday. I could have one on Saturday.
I snuck food whenever I could because I was constantly hungry which only made my parents more desperate and guilt-wracked, which only made me find more creative ways to sneek more food.
Because my mother was overweight, she got and took a lot of unearned blame for my weight. The blame only made it harder to get to the real issue - the metabolic and biochemical issues that were causing what I eventually (as an adult) would come to call the "rabid hunger" I felt all the time.
There were signs that I was carb sensitive (perhaps even carb addicted) and had insulin/blood sugar issues, but noone at the time thought to test prepubescent children for blood sugar issues.
Once a month or so, my parents would take us for donuts after church. Even as a small child I has learned that I couldn't eat sweets for breakfast without getting sick about 20 minutes later. So while my brother would have a huge filled donut, I would just have 1% milk. I could pick a donut or two, but couldn't eat them until later in the day (and I would pick french crullers because they were the lowest in calories and sugar).
Even today we have never had any overweight kids in the family besides me. In fact, no one under the age of 26-28 has had a weight issue. On my mother's side the women gain weight in their late twenties (and almost exclusively in the butt and thighs). On my father's side, everyone is slim, and noone is even a little overweight until retirement age.
I think assigning blame and fault only makes the problem harder to address.