Why is obesity and related behavior (overeating, choosing unhealthful food, eating more than your metabolism needs/can handle) something which is perfectly normal and out of an individual's hands while nicotine addiction, drug use from mild and largely non-addictive stuff to hard drugs, alcohol consumption, &c. are terrible things that make people evil by association?
I don't hate people who have addictions. I know plenty of smokers and ex-smokers. I know alcoholics (My stepmother is one) and former (and current) meth-heads. I don't villainize them, but I recognize that their addictions are bad and encourage them to seek help. Just like with any eating disorder. Some people don't have eating disorders, they just can't lose weight. Some people develop eating disorders like anorexia or bulimia because the desire to be thin is so ingrained by our society and they've tried every other way to get thinner. Eating disorders are bad. People with eating disorders don't have to be.
There's a really beautiful false dichotomy here, though. Why are the only options self-inflicted Evil and moral-obligation Good? I prefer to approach all those drugs you mention as bad shit happening to people, akin to diseases, and obesity the same way. So the gaining community (to the extent that it exists and isn't just Poe's Law rearing its ambiguous head again) can be compared to measles partiers, except those are fictional, so we'll have to find some other group that's just as stupid. But you've gone pretty hard to the opposite absurd extreme there, Flying Dice.
To clarify:
I don't particularly care about the vices that people choose to pursue, as long as they aren't substantially impacting the lives of others. I don't give two shits that my roommate smokes as long as he doesn't hotbox our room. I don't care if one of my friends drinks too damn much, because he's a happy drunk and doesn't try to drive. Stuff like that. But it's a pretty common societal attitude which worked as a jumping off point for the comparison; consider how smokers are being treated in the U.S., for example.
That said, neither do I think that it's a good idea to encourage people to falsely present unhealthy lifestyle choices as healthy. I also have an issue with the fact that it's rooted in self-deception; if you want to pretend that behavior that's killing you isn't, that's your deal. Don't try to spread it around and deceive others. It's also not particularly healthy (in a different sense) to try to absolve people of responsibility for their decisions. If I decide to start smoking crack cocaine, that's my fault. If I decide to start polishing off a fifth of whiskey every day, that's my fault. If I eat fast food for two of every three meals, that's my fault. It doesn't make me a bad person, but I shouldn't be allowed to tell people, "Oh, no, being addicted to hard drugs and being a functioning alcoholic is a perfectly fine way to live that won't negatively affect your life!"
Because seriously? Absolving people of all responsibility for their actions is even less useful than victim-blaming on the other end of the spectrum. Your comparison to disease is completely off-base, except in cases where people intentionally avoid vaccinating themselves and volunteer as medical aid workers during pandemics while not wearing protective clothing. The only people who could conceivably have these issues are people who gain them as children because of bad guardianship. Incidentally,
that is the single biggest issue I have with the stuff I've outlined above. American children aren't magically becoming unhealthily obese out of nowhere, and they're a massive victim group directly resulting from this chronic absolution of responsibility and labeling of everything as uncontrollable addictions.
At least it'll solve the problem with Social Security in fifty or so years, assuming the system lasts long enough to benefit from a large chunk of multiple generations dying before they can collect. :|