Some of the foods we eat are not as unhealthy as we think they are. Some of them actually contain the nutrients we require for survival while those healthy foods which we always think we should be having do not provide as much nutrients as they do.
Compare a serve of spinach to a serve of hot dogs. Spinach is indeed good for health because it gives you alot of the micronutrients. However, the hot dog, though seen as unhealthy, is in fact a source of protein, fat and carbs which are the basic nutrients we need for survival.
Yes we do need to consider the context we would like to compare both in. But the point is looking at our food in a different perspective and not limiting ourselves too much to the notion of healthy vs unhealthy food. As mentioned before, everything in moderation will lead to a healthier mind and eventually a healthier body.