It's a minefield, isn't it? What I do think is dreadful is blaming overweight people for their condition. I don't pretend to understand the many reasons concerning this issue, but I'm sure that poverty, the easy and cheap availability of foods containing unbelievable amounts of sugar, the culinary deskilling of three generations (for various reasons) and the increasing portion sizes served in pubs and restaurants has a lot to do with it.
Anecdotally, there must also be issues from early childhood which play a part. I have a colleague who is obese. She knows she is and is unable to do anything about it. But in conversation, she told me that one of her elder siblings was born with severe handicaps and when she was born she was sent to live with an aunt who had no children of her own. She was a very 'bonny' baby and then when the older sibling died, she returned to her parents. There must have been attachment problems as well as the over feeding and I think that must have contributed to her problem. Of course this not scientific, but I wonder if there are studies which show how early childhood experiences impact on later weight gain.