I’ve found a clever way to counter those folks is to say, “you might be right, and as the apex species it’s our moral obligation to seize control and protect the natural order of things for as long as we are able to slow the coming of hell on earth. Just like our right to shoot guns. Yee haw.”
Not all parasites cause severe food poisoning or make you sick immediately. They depend on your survival for their life cycle. When they make you sick depends on the parasites life cycle. He and Bella both probably could benefit from treatment for parasites.