Yeah, and we shouldn't blame cigarettes for cancer...I mean its the people who are smoking, it isn't the cigarettes!
McDonalds et. al. have engineered their food to be quite unhealthy (because it is cheaper) and then for decades they lied about that. In much the same way that cigarette companies lied about the health risks associated with smoking. Then, when they got called on it and people started to catch wise, both cigarette companies and fast food companies started targeting young people who don't yet realize that the hype is just hype.
Fast food restaurants are not solely to blame. But they share part of the responsibility. Also part of the responsibility is socioeconomic. There are neighborhoods filled with low income people where there are no decent grocery stores with healthy foods and the cheapest food around is McDonalds. If you are trying to feed your family on minimum wage, and McD's is there and no healthy food options are...and maybe you only graduated high school, and not a very good one...and you never actually got taught that McDonalds is a liar...and you get their ads saying they are healthy. Well, you may not have the tools to realize you are being deliberately hoodwinked.
It is easy to say, "Oh it is that fat person's fault" -- but doing that only allows us to ignore the larger structural issues that has lead to a wave of obesity in the US on a mass scale. And that obesity generally being related to poor education and poverty. I grew up in a decent neighborhood in San Francisco that had no fast food restaurants at all in it. Then when I moved to a poor neighborhood in Oakland there were fast food restaurants and liquor stores everywhere...and there was no organic grocery store and fresh healthy vegetables were not easy to comeby...unless maybe you had a car. But if you took your hoopty car to the nice neighborhoods to go shopping (if you could afford the overpriced products at Whole Foods) you'd probably get harassed by the police for being in the wrong neighborhood.
Health isn't just an individual thing. There are also larger forces at work.