For one thing, "harvesting human beings" is a ridiculously loaded and skewed phrase.
For another, being able to project probabilities stemming from changes is what trying to make life better is all about. The idea that one should throw that responsibility onto the lap of an imagined Bigger Viewpoint, to me, seems pathetically irresponsible -- why not just take on a bigger viewpoint oneself?
As for your fictional protagonist, he was not operating on reason. He was operating on a blind obsession, just as those do, for example, who believe sexual gratification is the whole sum of human motivation, or who think only money measures success. Human action changes things along a wide spectrum of areas and getting hopped up over one, to the exclusion of others, is a wee bit bent. Anyone will favor some areas over others, which is one of the magical flavorings of life, but extremism is yewgly whether it is religious or --for example-- eugenic in its rationalization.
As for absolute moral rightness and/or wrongness, there is no such critter available to use as a standard. Postulating one when there isn't is of course just childish. There is one thing that CAN guide us, if we learn to use it well, which is the human capacity for reason and compassion.