That's a good argument if you were to construct the world from first principles. You wouldn't get the current world order, certainly. But just as arguments against, say, nation-states, or multi-national corporations, or what have you, do little do dissuade believers, the same applies to let-the-natural-order-of-things-proceed advocates. Inertia is what it's all about. The normative power of the present state, if you will. Never mind that "natural" includes antibiotics, but not gene modification.

This may seem self-evident, but what I'm pointing out is that by saying "consider this world: would you still think the same way in that world?" you'd be skipping the actual step of difficulty: overcoming said inertia, leaving the cozy home of our local minimum.