There are far worse foods out there which claim to be healthy - have you read the back of those probiotic drinks or the average kids cereal?
At least with McDonalds you know they aren't very good for you and they don't claim to be.
There are good food choices there too - you can have oj, carrot sticks, salads, porridge etc. But you aren't supposed to eat them every day.
Would there be outrage if say, Thorntons wanted to adveertise? Or Alton Towers? It's a treat and you can decide if it's for you or not - we're not idiots, we don't need to be policed because our poor feeble brains are too addled to know when something isn't healthy.