My thought is we are built for our world, you try tinker with the natural processes bad stuff will likely result. We know a lot about how we function, but we don't really get the big picture of how everything here on earth works with us and we with it.
We're actually pretty intelligent, though, and we don't need to know how everything works together in order to be able to tinker with natural processes just enough to keep from dying, in a lot of cases.
Keep in mind that a healthy percentage of the people reading this discussion would be dead right now if it weren't for modern medicine. I've personally had several bacterial infections as a child that would have stood a reasonable chance of killing me if it wasn't for antibiotics, and one nasty infected wound as an adult that I was told would have had me at 50/50 if it wasn't for the meddling that doctors were able to do to clean it up.
