the natural population controls are disease, famine, and war. if we want to control population the natural way, we can wait for one or more of these factors to do it for us. conversely, we could choose to limit population growth ourselves.
it's a sticky issue. limiting it ourselves means that some external agency will be determining how many children a person can have. however, if we don't do it, it's a certainty that our descendents (possibly only a couple generations from now) will be dealing with even greater, natural forces which are unelected and quite a bit more terrifying.