Obesity to the level we are talking about (not just 'letting yourself go' meaning some fat around the waistline) is most definitely almost as bad as anti-vaccers.
By allowing themselves to become so large that they have trouble walking on their own, they slow down public transit, get in the way of everyone else, clog up medical centres, devour far more food then they should, are slow at work and less productive then fit people. Im sure there are other examples i'm missing but it doesn't matter, what does matter is that by allowing themselves to become that obese, these huge people have become a genuine drain on society with very dangerous, damaging ramifications.
You say that being overweight isn't on par with the negligent murder of children so lets return to the medical aspect of being hugely overweight. Once again, it is a drain. Huge rolls of fat make it difficult to perform surgeries, diagnose genuine problems and cause these genuine problems constantly. Have you ever tried moving 200kg+ all at the same time in a massive, doughy container? I imagine its not easy but I digress.
Lets have a hypothetical situation: Say an obese person rolls in to a very busy ER, they're having a heart attack brought on by their terribly unhealthy eating habits and attitude towards exercise. The few remaining doctors not currently embroiled in other things rush to help and they take the Obese Person further inside, bare in mind that this situation was brought about entirely because of the Obese Persons lifestyle.
Next to come in is a fit, young girl who has been the victim of a stabbing, something she had no control over. They do what they can for her but because all the experts are tied up elsewhere and the remaining doctors who COULD have helped are now with the Obese Person, this girl bleeds out and dies.
By being so obese that they caused a medical situation for THEMSELVES the Obese Person in this situation is one of those variables that is directly responsible for the girls death.
(Of course im not a doctor and that situation was pulled entirely out of my arse, take it how you will.)
TL:DR Allowing yourself to become so overweight that they need to invent a new word to describe you (super-obese) is exactly as bad as anti-vaccers if not worse. This is because super obese people are a drain on public infrastructure in every regard.