I have listened to some fat people and what they tell me suggests that I don't know everything about them nor the problems they face. Of course, being a former PE teacher and now gym owner makes me feel I can help them lose fat. It is just not that simple. Many fat people have fluid retention that makes them heavier but is not fat, per se. I suggest you frequent Dimensions Magazine forums and educate all those 'ignorant, weak-willed' fat people.
Like you say, many obese people are harassed and ridiculed over long periods of time. This leads to a low sense of self worth and self confidence, which again often leads to lack of belief in oneself, and lack of both will power and discipline.
But that is not the point. You justify empathy for obese people with medical data that does not exist.
Mental issues can be just as challenging as the physical ones, yet feeling sorry for fat people and justifying their false reasons for being overweight will not help anybody except creating a bit of relief in the short run.
99% of fat people can lose the weight IF they get their mental issues handled. It is that simple. And the general consensus among fat people today = "it is not our fault", which is another form of saying: "I am a victim, please give me some empathy". Might feel good there and then, but it will not help them fix the underlying issue.
Even if fat people had a few extra medical problems losing weight, it would not mean shit if they got their act together. Problems means nothing once a firm decision = made. (Gary Buseyism)
Therefore good old Vince: Calling Getbiggers not feeling "sorry" for fat people ignorant and immature is pr. definition an immature act in itself.