Let's not reduce the burden and overcoming of being overweight into one yes/no variable - choice. Clearly as we've seen by some of the testimonies, the reality is much more complex and I feel that some of the reductionism going on doesn't do the situation and the people going through it justice.
Even choice is a lot more complex than a yes/no decision, there's a huge range of behaviours that we could pin between choice and "non-choice", so it's more like a spectrum. There is also a string of individualism going on, which also ignores and begs the question of what society and the environment has on influencing one's actions. Sure, at the end of the day said person makes a choice - doesn't particularly help anyone though.
I also don't find using imperatives in threads to be courteous, no matter to who it's directed to. It goes back to the primacy of positive thinking - confrontation leads to nothing beneficial. You could tell someone going through something difficult that it's their responsibility, but to be honest, that's just stating the obvious and aggravating their frustrations and lack of self-confidence further. I find that when people are encouraged in a positive environment, they tend to confront their demons on their own, without anybody telling them to. Likewise with the issue of choice, there is a spectrum between encouragement and molly-coddling and we shouldn't be so focus on just one of the ends.