I don't know if you're right or not.

I suspect the basis for your theory is the idea behind inoculation. However, the purpose of the kidney and liver are to serve as filters for toxins. In any other context, filters don't get stronger with use, they degrade with use. The more crap you shove through it, the faster it degrades. How often do you have to change your car's air/fuel filters, or your HVAC filter? How often do you have to change them when you abuse them by living in a dusty climate?

Thus, my own (unqualified) take on it is that these organs can only handle a finite amount of filtration before they simply fail.