"When we get overpopulation of, say, elk, we can bring in the wolves or bring in the hunters.  The only thing that is going to stop us is virtual destruction of the planet's ability to support us."

Since there are no longer four legged "wolves" capable of culling human population, human wolves long ago took up the  function. From Sargon through Ghengis Khan to Hitler.    

When you run the numbers, the record of "human wolves" in controlling our population isn't all that good.  WWII caused a total of 60 million deaths or so, over about 6 years - say ten million per year.  Our current excess birth rate is seven times that.  We would need seven simultaneous conflicts on the scale of WWII, continued in perpetuity, to control the population.

The only wolf capable of mustering that kind of ongoing death rate is that old she-wolf Mother Nature.