Ants are an essential link in the food chain. There's no telling what effect the uncontrolled killing of any particular life-form might have on the balance of nature.
Where I live, we've inadvertantly killed off all the natural enemies of deer, so they proliferate like rabbits in Australia. Therefore they must be hunted, in order to control their population and the consequent damage they can do to vegetation, which is their main food source. I love the deer. They are beautiful, gentle creatures, and several mornings a week I see them grazing in my yard. However, we have done them no favor by killing their natural enemies.