Substitute humans for the foxes, then. Imagine humans were totally dependent on rabbits for their nutritional needs. Would you argue that it's right for the human race to commit suicide through starvation, to avoid killing any more rabbits? What about the extermination of our entire species? Would the human race have no moral value, if we were obligate rabbit-carnivores.

IMO, few would lose much sleep over the rabbit slaughter: humans value other humans far more than we value rabbits.