Obesity isn't an addiction, you can't be addicted to food..at most you can get cravings due to the sugar and additives in the foods that make you obese.
If you are obese, there is a reason for it beyond the just eating too much , eating poorly and not exercising.
More often than not there is a mental health reason behind it, such as a trauma, grief, depression, anxiety, self esteem.
What this means is that slimming clubs and diets don't work, because it's all about the food and exercise. They are not concerned with the ' why'. They think it's laziness or ignorance.
When I went to a counsellor and discussed my inability to lose weight despite all the negativity ,and complications it caused me and family, she talked about desire and self esteem, and how I felt when I had the food I knew was contributing to my obesity. For me it was power. The only thing I felt I had control and power over. I want this so I can have it. The ultimate goal is to replace the feeling you get from food with something healthier.
The OP asks why it isn't vilified and why people are OK with obesity..well I don't think they are. I think anyone that states that they are happy being fat is not being honest with themselves. There cannot be one obese person that would rather be a healthy weight.
You cannot compare obesity with an addiction like Alcohol, gambling or drugs. It's a serious issue, but a different one.