Ok... so say your car is running poorly. THe "cause" might be that you have been giving it the wrong grade of gasoline for several years. THe "symptoms" are that the car wheezes and the fuel filter is clogged.
So, according to your suggestion, treating the "cause" only would mean switching gas. HOWEVER - you still have clogged fuel filter! Do you just ignore that? No - because the car will keep wheezing until the gas flows freely. You have to CLEAN the fuel filter AND put the right gasoline in the car - only THEN will the car run properly!
Our bodies are like cars in a sense -- we are a system of tubes and filters. ANd when our filters -- liver, kidney, etc - are clogged, we don't run right.