Some random thoughts:
Female rapists are very much rarer than Female murderers, or male rapists.
Murder can be a very instantaneous act, done remotely. Can be a moment's loss of control. It may not have much additional violence, though can have.
Rape requires intimate personal involvement, violence, restraint and probably takes longer.
But actually many countries give much lesser sentences for rape than murder. Unlike murder there is often a suggestion the victim was consenting and changed her mind later. Or wanted "rough".
There can be many "degrees" of Murder from well planned premeditated, drunken rage, to the accused being cleared, (involuntary manslaughter) even though the accused has the smoking gun / bloody knife and found standing over the dead victim. Rape either is rape or it isn't. The amount of violence isn't a guide (drugged victim vs consenting adults that erm... )
Actually it can be harder to get conviction for rape? In some countries nearly impossible?
So is it true that people forgive murder more easily than rape? Or does it depend on the motivation, circumstances and relationship to victim?