I've been underweight and I've been morbidly obese. I'm currently at a healthy normal weight.
The situation in the United States in particular is really unfortunate. Being entirely sedentary and overweight is the norm. Go into a supermarket and you'll see people loading up on Coca-Cola and tortilla chips, liters and liters and bags and bags, filling the shopping cart. It's unlikely you'll see that cart dominated by fresh produce unless you go into a Whole Foods, where well-off people spend half their paychecks to feel good about themselves.
I don't blame these people who go from point A to point B in their cars and eat junk and fast food, because they're just living the lifestyle our society has created as the default. Breaking out of that mold is not just a matter of willpower, it requires education. People are being told so many contradictory notions about fitness and health, how can you expect anyone to know whether what they're doing is healthy or not? And when most of the food options in any given area are either fast food like McDonald's or Taco Bell, or hypercaloric chain restaurants like Chili's, or supermarkets with countless aisles dominated by unhealthy but easy options, why should the expectation be that someone is going to eschew all of that entirely?
I'm not going to condemn fat people as lazy. In fitter European countries, everyone got around on foot or on bicycle by default and I was never overwhelmed by garbage fast food options. That alone is enough to allow for a much slimmer society, but the United States was designed around the car, and the horrors of fast food nutrition came about in part due to the requirements of supplying national chains across vast distances.
A lot of people can be turned to the path of fitness and health if you actually give them an outlet for their willpower and frustration. Tons of people ask how I lost the 120 pounds and staved off the eventual wheelchair and type 2 diabetes, glimmers of hope in their eyes. Other people don't give a damn about whether someone's going to need to get a wheelbarrow in 20 years to get them to Wal-Mart, and that's their prerogative, but I obviously have less respect for willful apathy, as with any facet of life.