Much of what we experience as disease is self-generated. We have polluted the air we breathe, the water we drink, and the land we cultivate. Even many of the fruits and vegetables we consume are contaminated with chemicals designed to protect us from insects or spoilage. If we haven't polluted it, we have managed to strip it bare of all nutrients and, in some unfortunate cases, all oxygen-rich vegetation. Portions of our Earth are barren and no longer.
Plants are hybrid, genetically altered, and no longer reproductive.
Water experiences so many protective purification processes that it doesn't even taste like water anymore. But, humans are a very adaptable species. We probably can and will survive most of our damage. Unfortunately, there is one detrimental contrivance we may not survive. Stress, the most self-destructive thing we have managed to bestow upon ourselves.