I do find it concerning just how many people talk about things like this without ever challenging their fundamental understanding of social norms. A lot of you do just assume you're smarter than me, which is funny, and I wonder if you've ever actually read anything on fatphobia and the arguments for its recognition.
Bigotry is difficult for liberals to understand because they typically want to recognize it as individualized actions of aggression like calling someone a slur or being mean about someone's weight. Have you considered for a moment that you are vulnerable to the laundering of values that promote dehumanization and genocide through vectors of "bigotry" which you don't take seriously, such as fatness? You used the word "curable," which is very convenient for me as it is a good demonstration of how this topic is medicalized (we can ignore the well-documented discrimination against fat people in medical settings for now), and specifically how it is pathologized. When something is pathologized, that means that whatever is seen as wrong with it is always relative to an idealized, "positive" thing; a fat body is bad (unhealthy) because it is not good like a thin body (healthy). Regardless of the medical science behind this construction (of which I'm sure you also have not read as it is well established by this point that fatness is not necessarily unhealthy relative to other factors), this has manifested socially as a vector of discrimination exactly because of the perception that this is an illness that is cured by willpower. Conveniently in an neoliberal culture, an illness that materializes laziness, poor self-control, and general moral degeneracy reinforces an individualism where individual people are responsible for the effects of their material conditions; i.e. you can choose to be fat the same way you can choose to be poor.
Because fatness is not a recognized vector for discrimination in the same way that racism and sexism is, it is an important site of scholarly discourses exactly because of how effective it is at laundering ableism and classism; along with the fact that it is a measurably oppressed and vulnerable group based on the research I allude to above. Liberals like you don't question any of this, and then readily engage in the fascist rhetoric I am criticizing in this comment with the assumption that you are doing the righteous thing by promoting bodily health and dissuading any claim that a person's fatness is not related to their moral quality of character. It is not about, "body-positivity" any more than anti-racism and anti-queerphobia is even though those forms of oppression similarly relate to the subordination of particular bodily attributes to others. That oppressive ideal of thinness is inextricably linked to ideas of whiteness, and "fitness" in a very fascist understanding of the natural world and human evolution.
Hope that explains some of it to you.
This one is way more zealous than the other one, refer to the other comment for an explanation of the connection.
It isn't that it's mean, you dummy, it's that the underlying values of this joke are in fact fascist in their orientation and, because people like you exist, it is an effective way to promote those values. If you need an example, think of the jokes about these people that reference inbreeding with the presumption that it is correlated with poor intellectual and cognitive ability, and therefore validates the idea that these moral qualities are related to genetic qualities (there is also a classist element in this joke given where they are oriented in the US geographically). Even if there is science to suggest that this is potentially a real consequence of inbreeding, I hope I don't have to explain even more clearly to you why it is problematic to naturalize the correlation between genetics and the danger one group poses to society at large.
You've tried to lecture me on language, but you don't seem to know what any of these words mean, which is why you are so vulnerable to the manipulation that they promote. You think every fascist is just what, dumber than you? You don't think that maybe there's a way to "trick" you into subscribing to the same values they do, especially if you already subscribe to liberalism wholeheartedly as what appears to be the case here? You don't get to choose the consequences of your actions, you can only inform yourself so that you can make better decisions in the future. If the effect of this joke is that it reproduces the idea that there are physical markers for moral depravity, then you either have to admit that you want it to have that function or change the way you understand these terms and the context they exist in. Some fascists choose to be fascists, most of them just don't think about it.