With a few exceptions that include other medical conditions obesity is a self inflicted condition. It is not a disease. If you consume more calories than you expend by physical activity then you will gain weight - that's a fact of life. Eat too much and exercise too little and you'll get fat. Do the reverse and you'll lose weight. It's a simple formula that millions of people have learned to deal with but it still also seems to have been missed by others.
Yes, there's more to it than that (http://www.who.int/features/factfiles/obesity/facts/en/index.html), but the basic premiss is still true.
We should not encourage people to think of themselves as victims as instead empower them to make the right choices to live healthily and to manage their weight. Otherwise they risk suffering a long list of medical problems caused by obesity and dying young. Obesity is costing the health services billions in extra car. Just putting up with the situation and making allowances doesn't help. Airlines have every right to add a premium for passengers who can't fit into their standard sized seats. Other passengers and crew should not be expected to just accept without question what is mostly a self inflicted condition.