While I respect what you are trying to do, I think your view point is somewhat skewed. Most of the better cleanses out there are fiber based. Not a laxative, and therefore little chance of dependence (I would not reccomend senna for that very reason) Regadless of what the establishment might think, you are not taking into account that the vast majority of people don't get enough fiber to begin with which leads to the buildup of fecal matter on the colon.
Second, I agree that the human body is amazing at ridding itself of toxins, but we have not kept up pace in our evolution with all the crap that poisons our bodies on a regular basis. These are pretty much too numerous to list, but I don't think cave men were eating fast food, pumping gas, washing their hands with antibacterial soap, using antiperspirents etc. So my unscientific opinion is that the body needs a little help once in awhile.
Lastly, with all science aside, I also know someone who is on the Natura colonix program and he crapped out soething that was the size of a bicycle tire made up of a rubbery fecal substance. I do not know what it is or was, but I bet the medical community would not reccomend leaving something like that in your digestive tract.