Stryder, I think I know what you are trying to say. Possibly one might compare the situation to the bacteria in our guts? It is well known that when we get an infection and use antibiotics for too long we kill the whole lot, bad & good. I can imagine a situation where we may have a few parasites that will not harm us so long as our lifestyle results in our body's ability to keep their numbers low.
I know that Andreas Moritz is opposed to the ingestion of parasiticides. His thinking is that there's no point in trying to kill them because they'll reappear in no time flat - and you can't go around constantly taking strong medicine. Moritz believes that we should keep the number of parasites low by keeping our bodies strong & healthy. Here are his words:
"Undigested food becomes a breeding ground for bacteria and fungi, parasites and worms. To kill the microbes is a fruitless attempt since this doesn't remove the cause of the problem. In fact, it may make it worse. They are just doing their job, as they do it out in nature. The more your fight them, the more resistant they become."
For my part, if I was in a weakened state and had severe infestation, I would - notwithstanding the above - try to kill the parasites. Later, I would change my diet and way of life so as not to attract them any more!