For myself I define bad processed foods as those foods that contain fake chemicals I can not pronounce, fake sugar, artificial colors, trans fats and genetically modified foods who's seeds must be purchased every season. I don't care for animal that have been fed antibiotics either.
We are messing with nature and it's similar to killing off one species and not understanding how that affects the whole, because we haven't evolved to the point where we understand the interconnectedness of nature. So eating all these fake chemicals can be affecting us and our children at a level we can't understand.