Fast food has existed for decades. It is lazy parents who treat fast food as a staple rather than a special treat that lead to a nation of fatasses.
Granted I am an old guy, but I just don't remember having fast food much when I was a kid. Maybe once a month my parents would get a pizza for dinner. We'd each get two pieces of pizza and salad. Not that we didn't eat out ever, but when we did, we'd go for Chinese food or Italian food and sometimes we'd split our portions. It wasn't for economic reasons either. My parents had ample money to spend on meals.
My wife and I raised our two children much like we were raised in terms of eating fast food. Eating at a fast food restaurant was a rare occasional thing and not the norm. My wife is an excellent cook. Our daughter, her husband and their son's mainstay is fast foods. Almost a day doesn't go by that my grandson isn't having pizza as a snack. Fortunately, he's genetically predisposed to being thin, like I was. However, enough fast food and he could start ballooning up like so many folks do.