Almost philosophical question about controlling a pest/plague
Biologists are certainly not afraid to exterminate pests and plagues in the wild. See: smallpox and polio. However, such exterminations are nearly impossible and very expensive. See: smallpox and polio. In both cases extinction is through  extensive vaccination, preventing the disease from having any hosts to live in. To achieve this you need to vaccinate a huge fraction of the human population for quite some time.

Practically, how would you go about exterminating an agricultural pest? A beetle, for example? Perhaps an army of men, forming a cordon the width of the united states, turning over every rock and every tree from the west coast to the east coast. With a high net or something to prevent beetles from flying over the cordon. And some method for dealing with cities and roads and tunnels and things, because if you miss only five or six they'll be back soon, depending on life cycle and offspring numbers. Or if you forget Canada. 

And to use a biological solution to a biological problem, consider myxomatosis and the Australian rabbit problem. Rabbits were(and are) a pest, myxomatosis is a rabbit plague that has a 99.99% fatality rate and is fiercely infectious. Sure enough, myxomatosis wiped out the rabbit population. A few years later the rabbits were back but now the survivors were resistant to myxomatosis. 

I would argue that it's a scientific thesis based on hard lessons biologists have learned about doing 100% of anything. There are many biologists with moral precepts against the extinction of pest species. It's a bit of a moot point, however. The only reliable method of extinction is habitat destruction. Whether that's immunizing all the humans or cutting down the rainforests, it does work. It's just usually impractical.