Is being fat unhealthy?: NO.
Can being fat or obese cause health problems?: Yes, but unless you are genuinely concerned about the person with the health issues, keep your shitty comments to yourself about their appearance and health, or, if you genuinely cared in the first place, your voice of concern probably wouldn't be coming from a place of ignorance or sound hateful and rude.
Who are you to judge what is or is not healthy for a person to be? ANYONE can have health problems. It's just so ridiculous to me that someone could see a bigger individual walking down the street or see them online and just assume that because they're fat, they're unhealthy and they're eating too much. Or that it's somehow okay to poke fun at them and treat them like shit like they don't have feelings or something because they're fat. Like, if you don't know them at all or what they've been through or deal with, why are you even paying attention to them in the first place or assuming things about their life?
Being fat does not mean you have health issues. I've known people who are fat who are 100% healthy.
If you know someone who is fat and it actually is affecting their health in a negative way, you should sit them down and voice your concerns honestly but don't be an asshole about it because hey, you can be honest without being an asshole.
If you really want to make jokes about obesity, that's fine, just don't do it at the expense of another human being unless they're 100% on board with it or you know it's a friend who will be just fine with it (I guess this could be said for any joke, but I still think there are some things that you should just not make a joke out of), but the joke about the people at the airport who smelled like sausages, and the kid you had to sit next to on the plane? That's just rude, and if affected a real person: http://tony-posnanski.kinja.com/i-was-the-fat-kid-sitting-next-to-nicole-arbour-1728933269
The fact that anyone would act like that towards a child for any reason is just atrocious. Especially if it's a child that you don't even know. That could really fuck a kid up.
People can be born naturally big, and their bone structure can be a reason for that. Maybe they have a disease that caused them to gain weight and makes it ridiculously hard for them to lose it. There are people who are fat that have tried everything to lose weight and it just isn't working, or they lost weight but had a hard time keeping it off. Maybe they're too busy to focus on losing the weight. Human bodies are complex and what works for you and improves your health and improves your life could damage someone else and their life.
Shaming a fat person with the hopes that it will motivate them to lose weight is the wrong way to go. Sure, it might help some people and if it does that's great, but it's a punch to the face for so many others. It's just plain stupid to be an asshole to someone for any reason and then wrap it up with "I'm just saying this stuff because I'm concerned and selfish, and I want you to be around forever" or call it "comedy" and act like that's somehow supposed to make it okay, or to act like those of which got upset by your words are somehow "killing comedy".
If someone is perfectly happy being fat or they think they're beautiful and love themselves regardless of their size, that's their prerogative. It's called a self esteem and you have no right to tear theirs down just because you think that what they are is the wrong thing to be.
Confidence is not "they will like me", it's "I'll be fine if they don't."
They're not there to please you. And they're not there to be a joke for you to laugh at. If they lose weight or aspire to lose weight, it should be because it's what they want, not because it's what they felt pressured to do.
So many people take the stress and sadness building up in them because they're fat and because they get shit for it and it turns into an eating disorder. They start to obsess over their appearance, their food intake and soon they're throwing up into a toilet after every meal just to have the appearance that you would see and think "now there's a healthy person" until they take it too far and soon you're saying "wow, you look a little frail there, maybe you should get some meat on your bones".
Or, they start to eat MORE as a coping mechanism because it brings them comfort and then they wind up developing an eating addiction.
Sure, fat people can have health issues, but more often than not, the people who shame them and make them feel like a lesser being for their weight are the ones giving those health issues to them.
Here are a couple of videos from Youtuber Trisha Paytas that I agree with: