I always feel that we should leave things alone, until something becomes overbalanced. Problem is when we have something like that we need good diagnosis.
This reminds me of the book and movie, "War of the Worlds". The aliens were taking over the world; and there was nothing that we could do about it. They were already parasites to us. We could not defend ourselves, not even with any army weapon that we had. Then, in the end of the story, they started to die. They were not immune to the bacteria of which we certainly were.
This also reminds me of when I was a child, stepping barefoot in fresh cow pies and squishing through my toes. I'm sure I became a great host to several undesirable tenants.
So it really is a story of balance for all our life.