McDonalds and most fast food is crap, but I still eat it now and then. In fact, I eat it most often when I go to a rocket launch. I get packed up the night before, and the next morning, I just roll out of bed, hop in the truck and go through the drive-thru. Get a large coffee with cream and sugar and two sausage McMuffins with egg. That's the fastest way for me to get on the road, and even though it is crap, it's a good-tasting breakfast, and it's pretty solid, and will stick with you for a few hours. After about an hour on the road, I stop at a Subway. The main reason is that by then I have to crap, but also, it's the last place to get a decent to-go lunch before the launch site. I get a foot-long sandwich, chips, and 2 bottles of Gatorade. That's my lunch at the launch and snack for the drive home. Sometimes I stop off for a bite on the drive back, and that's usually fast food too.
But other than rocket launches, I never eat that junk. If I get diabetes, I guess I will blame rocketry!
I liked the Spurlock film, Supersize Me. But I think the reason he got so unhealthy so fast was not just the fast food, but also the other rules he had set out for himself. He had been a very active and athletic person, and he gave up all exercise for the film. Also, he had a rule that if the cashier asked whether he wanted to "supersize it", he had to say yes, and he had to eat the whole thing. So he hadn't just changed the composition of his diet, he was also overeating by a huge amount, and he wasn't burning calories the way he had before. Just that alone, screwing up your balance of calories in versus calories out by a few thousand a day, will blow you up like a balloon in no time at all. The film was interesting, but I think it was an indictment of a lifestyle --- not just fast food, but also being sedentary and overeating.