Sugar is only part of it. Corn and wheat based products are just as bad.
The truth has to do with food availability as well, not just what it’s made of.
Food availability has increased in the US over the past 50+ years, to where we have over 4000 calories per person a day now. Easy access to unhealthy food is a major contributor to our obesity. People don’t even understand what a healthy diet looks like and have a very poor grasp on how much to eat. We just eat until we’re stuffed and then wonder why we’re fat.
It’s especially tough as people age. I’ve been tracking my diet for 180+ days, eating under 1800 calories a day, and I still struggle with losing weight. Without a lot of effort towards eating the right amount and the right foods, people get fat.