So first by in nature are you referring to the philosophical state of nature or the legit nature with rabbits and such?Your solution adds to a multitude of solutions, killing (ethical) and waste of more resources. Human lives already require the a energy consumption to raise (1st world) because they always need the best (the common mentality) even though in nature, we don't. If you kill already grown humans, you wasted all the Earth's resources into put into that person
Second over population does exist correct humans can solve it with other ways such as only growing vegetables in there native areas. But this would only work if humans could overcome there greed before the effects of overpopulation begin to present themselves.
Further in answer to your comment about wasting resources, this would not waste resources because it would lower the population to and level out the population to a more sustainable number allowing a decrease in need for resources insofar that there will be less need for war.