My father was a immunologist, with a PhD in microbiology. Back in the '70s, there was a stink about saccarin causing cancer. My father, who was definitely in the know, just shook his head and said, "If they gave those mice the same amount of water as they gave them saccarin, they'd get cancer from the water!"
Pure science requires flawless techniques, and pure science has no agenda. As humans are attempting to practice science, we will always conclude on something less. (Until five years from now when the conclusions will be different.)