I bet if you ask almost anyone in the world "Do you have a healthy diet?" they will respond they have a healthy diet. They probably will add that they eat more healthy foods than many of their friends and family. Try it, I did.
Further to that if you ask anyone in the world, "are they eating healthily?" I bet you would get a critical answer, arguing something like, "no they're fat aren't they", or "they don't exercise enough", or "look at the size of that diet coke!"
My point is we all (myself included) have an inflated view of our own dietary habits and are only able to be critical when it applies to other people.
Please bear in mind I am NOT talking about what one thinks about our diet inside our own heads. I am talking about what we are prepared to admit openly about.
Yes, we may admit to the odd chocolate bar or other treat, but do we see that as part of our diet? To be precise if someone asked you to keep a food diary for a week or two would you write the odd treat down, or perhaps because you were keeping a food diary for a period of time would you say, "no I won't have a mars bar on this occasion."
What's going on?