It's a fallacy to think that humans will never know disease if we live in some perfect state, drink water from mountain streams, eat vegetables grown by virgin nuns, etc. Disease is part of being alive, it happens and is mostly out of our control. Sure, don't smoke, don't drink too much, don't live on lard, Doritos and hot dogs, get exercise, go to the doctor periodically. But even when everything was done perfectly, we will all die and very few die from old age. Death happens, disease happens, cancer happens, prostate cancer happens. It's part of being human.