Killing is a bigger crime than non-consensual sex because killing eradicates said animal from gene-pool and ends its potential progeny/generation. We try to justify killing of innocent animals because we are beneficiaries of that injustice. Benefits is corrupting our sense of morality. As for Zoophilia, it's non-censensual sex, less harmful than killing. Killing is also considered a bigger crime (than rape) in jurisdiction of humans.