"and it behoves us to not blunder in and wipe species out for our advantage"

So preserve Variola major ?
How about Plasmodium falciparum ?
Moving along to the multi-celled how about Onchocerca volvulus ?

It doesn't take long to get to the mosquitos when deciding where to draw a line. They are a vector though. It's nice not the have the ague in the fens. Is local extinction OK if they are still plaguing others?