Why is rape a law in such less detail?

[xxXBattleofOneXxx]

Ok. Rape is against the law because it is against "the defendants" consent. Its not as if the woman says "yes, you can have sex with me", it just happens. However, murder is a certained crime because the person is of course, dead. What Im asking is, women could say they have been raped about anyone, just to get back at someone...There is no evidence at all if a woman has been raped. I hope you understand what I mean.. If there is nothing securely substantial "for" a rape crime, then why is it a crime? I know rape is definetly wrong and I think jail sentence is right for anyone who commits it, but Im looking at it from the "law" point of view.
*Why is rape a crime in such less detail"