I think you're in danger here of assuming forced rape with violent assault. But we know perfectly well a lot of other rape occurs, and I think some of that is something people can much more easily justify to themselves in the heat of the moment. Such as two people out on a night out, they're getting on well, one of them gets blind drunk and is taken home, where the other takes advantage. There are forms of intimidating people into compliance (think some PUA shit), and people can much more readily tell themselves that they had consent, or at least the facsimile of it that is someone not stopping them.
I think you're also looking at this very rationally, and overestimating the rationality of others. I've watched some real police dramas, and I was staggered to see some people, when the police have laid the proof of their sins in front of them, hopelessly protest that they aren't a rapist, or a child abuser. I don't think this is just some feeble last gasp denial as if the police are going to say it's all okay then and withdraw the charges. I think they simply have not managed to fully conceive of what they have done as wrong.
I think you're misunderstanding my point.
I'm not saying that people don't create excuses in their head for why something "doesn't count" as rape. I'm saying that everyone knows that rape is bad all the time as there is no moral justification for rape.
Like I said, with theft someone can say "yeah, I stole _____, but it was because I don't have any money and it was vitally important to my well being." This wouldn't necessarily be a legal defense, but one would not say that what their did was immoral.
With murder someone could say "yes I killed that guy, but it was because I feared for my life" and even if their self-defense claim is legally imperfect, the murder may not be seen as immoral.
There's no such justification for rape. You would never hear someone go "yeah, I raped her, but it's because I was really horny and she wasn't putting out" and for people to go "yup, sometimes that's ok."
People don't try to justify rape, because there isn't a justification. They try to justify why their actions weren't
actually rape, or why there isn't enough evidence to prove that what they did was rape, which is a different argument altogether.