I'd take issue with that, actually. I probably wouldn't fit into the rides at Alton Towers, but I'm in good health. Yes, I need to lose weight and am doing so because of the health issues that can come with being overweight, but being fat doesn't automatically mean being unhealthy.
There are a number of reasons why someone of my size would find it hard to lose weight. If it were as simple as "eat less and move more" then we would all be size 8 ... but it isn't always that simple, particularly if someone has a significant amount to lose. There are often emotional issues that need to be overcome - just as there are with other eating problems. Until those emotional problems are addressed, the weight won't shift - and if it does, it won't stay off. Plus food can be an addiction, just like any other, and can be just as difficult to break as any of the more accepted forms of addiction.
For many people, myself included, there's self-worth issues tied in with weight as well. When you have poor self-esteem, you can feel that you don't actually deserve to be slim and healthy ... I was able to eat well when I was pregnant and my baby was at risk from gestational diabetes, but I can't do it as easily for myself because I don't value myself as much as I valued my dd. It's really hard to explain to someone who hasn't been there, but there are other things in the equation along with eating and exercise.
I don't want society to "accommodate" me (probably just as well, given the attitudes that some people have); I know that there's only one person to blame for my weight, and that if I can't fit into a ride at Alton Towers it's not the staff's fault (although, like the ladies in the programme, I would be annoyed if I'd been assured that I would fit into the seats and then found I'd wasted my money). What I do want, though, is to be seen as a valued member of society on my own merits, rather than because of what the size label in the back of my jeans says, or whether I can fit my arse into an airline seat.
To be honest I really can't see why this causes such strong feeling in people who aren't affected by weight issues. My weight is my problem and mine alone; it affects me (and possibly my family) but it doesn't affect anyone else at all ... why are people so bothered by it?