Firstly of note is that the closest genetic/evolutionary family of humans, namely the chimpanzee, also engages in an activity once thought to be uniquely human: namely warfare. And just to forestall all the anthropocentric qualms: it seems it is not our fault.
Secondly this tendency to own-species violence might be implicated in the evolutionary process. Homo sapiens may be what it is today because of developing some murderous instincts in the distant past.
It should not be overlooked that the reports cited leaves much room for subtleties such as in-group versus out-group violence and the complexities of the motives. For instance humans display less in-group violence than chimps while achieving stupendous levels of out-group carnage. The take away here is that: 1) humanity isn't alone in organizing a group of own-species individuals to do deadly violence on another group of the same species. And 2) there are evolutionary pressures involved in this behavior, that is, greater social interaction is a driver for greater brain development.
So now we come to the 'ethics' part of this question. Humanity has set itself to the preservation of "Nature", conserving as much of species that politics and economics would allow. Yet the human condition is proof that existence is more that mere survival, it is Art, and Beauty, and transcendence... Does it not follow that we should afford all species every opportunity to evolve to the best of their potential?
Now to make our failure plain through the case study of chimpanzees: we have given them space to live, to survive, but have we given them space to fight? To learn cooperation among themselves? To war? To learn cooperation amongst communities? To learn peace?
If humanity cannot afford its closest relative the chance to reach the next evolutionary milestone. How dire is their failure to allow Evolution to take its course?
Isn't there a conflict between conservation of species and conservation of natural evolution?
Question: Has anyone taken up this line of reason as a critique of human efforts at conservation?
Consider a more extreme example like cattle, the species could be considered one of the most successful ever in terms of population and distribution. But their "adaptations" are forced to suit human needs, were we to return a few cows to the wild they wouldn't be likely to survive. Humans have taken away their evolutionary potential.