I have another idea. Getting cancer in the first place proves two things. We were exposed to something that causes cancer, and our milieu interieur is primed to make cancer grow. This makes it simple to avoid cancer. Sure, we can't avoid all the possible causes we know of or not, so we can't really be sure we'll be safe if that's how we go about it. The easiest and best way to avoid cancer therefore is to make our milieu interieur as hostile as possible to cancer. Of course, if we work under the paradigm that cancer can only be beat with very toxic procedures, we'll end up killing ourselves in the process. But if instead we work under the premise that normal metabolism is that cancer-hostile environment, we got it made easy and painless.