Show me evidence that man used birth control for 300,000 years and the argument about western birthrates might have bearings. Otherwise, current birthrate is completely irrelevant.
Don't be thick. Life was much more iffy 300,000 years ago. Human beings, regardless of their beliefs, are not the top of the food chain. In addition to predators, disease, malnutrition, whatnot, took their toll. If we were to extrapolate your calculations to other species on this planet, we should be up to our eyeballs in flies, rodents, and guppies.