Devil's Advocate on Moral Utilitarianism: Killing a mite produces pain and disables a Qualia\ kills a sentient being. fucking a corpse is ethically use of an object -notwithstanding "property rights" ,ie; relative's feelings. but that's accessory and not intrinsic to the fact (For example having a T-shirt of a panda isn't immoral but if you wear it to a PTSD therapy group of panda survivors, it can be considered an Accessory Argument for immortality of that same action) .
So, ethically speaking fucking corpse is ,in itself, merely an erogenous use of an inert item, however killing a mite is actively using violence and pain-inducing measures to kill a sentient being with no value produced, not even hedonic value (which can presumably be obtained through erogenous stimulation)