Or instead of not eating boxed food, just do a research how much "bad stuff" in it and divide accordingly to meet your calories and nutrients target for a day.
by "bad stuff" i meant fructose, sugars, fat, etc. (i hope proteins are not blamed)
Americans are lucky to have all of it stated on the packaging, which allows very precise control of nutrients consumption. So if you bought box of Devil Hole (which are delicious!) and read, that one hole comes with 120 calories - eat just one! That simple.
Now... if you can't stop on one, this is completely different issue.
It's as much about habit-forming as anything. If you just stop buying food that comes pre-packaged, you force yourself to make new food-buying habits that will trend towards healthier meals.
Plus, when you're consuming the "bad stuff" it's even more difficult because of their interactions within the body.
If you can manage to research and control "bad stuff" in your diet and that works, go ahead. But why have them in there at all messing everything up?