Well, they start with this premise (" It’s a choice. (Never mind that diets have about exactly the same long-term success rates as ex-gay ministries.)") that being fat is not a choice. After that it's a series of dominoes, all resting on it. The #1 reason supporting it is "(fad) diets don't work", therefore, presumably, nothing can. Diet(1) (ie, a special diet people go on for short period of time to lose weight) has totally overtaken the original and primary meaning of diet(2) (ie, what people eat). Say "diet" to someone, what is the first thing they will think of? Eating normally (balanced and in appropriate amounts) is not a diet(1). It's like 1984. Words mean things we agree on, making communication possible. So when you change the meaning to be ambiguous or even opposite, you pervert language.