Suppose it is objected: Smith may want to kill Jones in order to take his goods.
But Jones likely values his life far more than his material possessions and would to that extent be willing to defend himself more ferociously. Smith puts himself in more danger if he tries to kill Jones rather than merely rob him (say, by quietly burglarizing his house).
The killing is, ahem, an overkill. Again killing seems in the interest of no one at all, an act of pure destruction, and for that reason is unequivocally morally prohibited.
Assault is proscribed for similar reasons as murder: Jones feels pain from an attack on his body, but Smith receives no pleasure as a result. The evil of being hurt is accompanied by no plausible good and is to that extent 100% morally wrong.
Rape is more difficult to outlaw on this argument alone. For the rapist may say: “My good is promoted by the sexual pleasure I receive and by the child I beget.” Here we may need to use further argumentation.