I think it's just something people are sensitive about, and understandably so. Most obese people (by choice; i.e. self admittedly just have a bad diet and sedentary lifestyle) I know are never really offended by memes and consistently express a desire to do better. Fact is fixing the problem is genuinely difficult once you pass a certain point, as it requires a dramatic lifestyle change. Anyone who says that is easy is full of shit.

I avoid jokes like that mostly because it feels like punching down on people who are not happy with their health/weight and struggling to fix it. Especially when it's the typical low hanging fruit, it's just not fun when the joke makes me feel like kind of an ass.