When I was young (60s and 70s), we had no car. There wasn't much to do, not a massive range of opportunities like there is now.
We NEVER went to a restaurant - I remember going to a Wimpy when I was 17 and being upset as I didn't now what to order or how to cope. I lived in the area where the first ever MacDonalds was opened, never went in there as it was too fancy for us 
I worked two jobs, nights off were for dancing, we walked or got the bus everywhere. My mum and dad both worked, we never had a car, my mum cooked a meal every night with meat, potatoes and vegetables. Sometimes we had tinned fruit and evaporated milk on a Sunday.
There was, literally, no food. Nothing in the house except bread. There were no snacks, treats were at Christmas, I was given only dinner money so nothing for crisps etc.
Our kids' lives are nothing like that now - are they?
And yet I was considered fat. I was one of the few people, apparently, in the whole world who were fat. Eventually I was a (then) size 14-16. Weighed 11 stone at age 16 and I was 5' 4". I was bullied at school, people would talk about me, shout at me in the street, family would confront my Mum (my adoptive parents). But apparently, the only way to be fat is to eat too much and be lazy and have fat and lazy parents.
I reckon we are on the verge of discovering some unpopular truths about obesity - maybe in my lifetime. But when I say we, I don't mean on Mumsnet. It seems very important to many Mumsnetters that they get the opportunity to have fat people as something safe to look down on - a reliable punch bag, a deep seated need to look at the fatty and say you are less than me. We need to view obesity as an illness, not a moral failing.