Detox/cleanses do have value, but not in the sense that it will be a quick solution or an "absolute cure". When doing them you can feel either great or not. In regard to "devastating", it could be greatly attributed to "upsetting the balance" or doing too much when the body is in a weakened state.
I think viewing the body as "dirty" is a matter of perspective! Would that mean that the body is "dirty" at conception, at birth, growing up, or now? If you think about it microbes of all sorts are everywhere! Maybe it's a matter of allowing an opportunity to grow and fester (because the opportunity is there)? Something to think about...