The people saying it's not a problem or that it will sort itself out are missing one crucial point - all the solutions for maintaining and/or stabilizing a big population require technology, which requires a technological civilization to exist. A technological civilization is not a stable, natural state, and industrial plants do not grow on trees. If the growing population destabilizes - let's be frank, Western - civilization, the world is fucked. The population will bounce back, with billions dying from hunger and war.