I can tell you this, ridiculing and shaming someone will most likely not result in motivation for them to lose weight. On the hand, enabling and lying to them will also not provide them with motivation to lose weight. There has to be a middle-ground between the two. Granted, people have every right to make fun of them (freedom of speech, blah, blah, blah). But from a motivational perspective, it rarely works.
Think of anxiety and performance. Research shows that there needs to be an optimal level of anxiety for peak performance. Too much anxiety, and your performance suffers. Too little anxiety, and your performance suffers. Think of bell curve (that meaty portion in the middle is the optimal performance of anxiety; too far right or left, and performance suffers).
I think the same thing would apply for people losing weight. Too much shame and humiliation won't work; too much enabling and lying won't work. You need to provide them with something in the middle.