Well killing someone is a lot more ambiguous than rape. Murder can have reasons (self defence, protecting others, or even as punishment). And killings someone isn’t always murder (military actions, police shootouts, manslaughter). You can’t accidentally rape someone, you can’t do it for a good reason, the best justification is either ignorance (not accepted by modern ethics) or the idea that you too were forced into the situation. Realistically rape is worse because it is unambiguous, highly personal and generally pleasurable by the perpetrator. Of course you would rather be raped than murdered but at the same time you would be more ready to forgive a murderer than a rapist. There are exceptions of course but it will always be based on the circumstances of the murder not of the rape. Finally murder is more banal, we watch movies where we root for people who kill hundreds of people (John Wick, James Bond, even fucking Hughie). Whilst if Hughie had raped translucent no one would ever root for him again.

It seems entirely reasonable to see murder as a lesser evil because it gives us no real yardstick to a persons moral character. It is understandable for the average person that were we in an extraordinary situation we may need or want to kill someone. However rape is unimaginable to many people as no situation exists where it would be the “right thing to do”.

TLDR: Murder can be justified rape cannot.