They engineered themselves this way with the Tekne, they have no excuses.
They engineered themselves so as better to pursue drives which were already dominant in their culture. I imagine that making pretty much everything sexual was a primitive trait for them, not a derived one. They may have made themselves even worse in the process, yes, but it's hard to imagine any slope being slippery enough for a human like species to modify themselves purposefully to enjoy raping infants to death on a species wide scale. Conversely, animals that have very poor fidelity in terms of choosing mates, and for whom mating is almost always rape, exist in the real world.