Infact, you argument seems totally at odds with the law. Are you saying a jury is instructed or acts upon what a defendant may or may not think and not the evidence?
I'd suggest under such logic many people found guilty "think" or "justify" illegal acts, that is not a basis for defence, perhaps mitigation, but not guilt or innocence.
Lets start with Morgan! One night he said to his mates, "Come on back to my place, and give the wife a seeing to! Her fantasy is being raped. She'll kick and scream a bit, but that's all part of the role play!" So there they went and that they did. The daughter climbed out of the loo window, eventually, and went for help.
In those days a man could not rape his wife, but Morgan was convicted of the offence, as an accessory to his mates' raping her. His mates claimed in their defence that they believed the wretched Mrs Morgan was just playing, and really consented.
The appeal decision was that if the jury had thought that they might have believed this story, then that that was a defence, but that the more unreasonable such a belief looks, then the less likely it is that a jury will believe it, and in Morgan's case the jury didn't believe his mates, and they went down for a long time.
In English law the prosecutor has to prove his case beyond reasonable doubt. I've often ended my spiel to the judges of fact, "...and, if, in the end, you think that my client is probably guilty, then it will be your duty to acquit him, because 'probably' isn't 'beyond reasonable doubt' " Where the offence laid down in statute specifically includes a mental element the jury has to decide what the accused was thinking. Look at the difference between "unlawful wounding" and "wounding with intent"! The same injury, either a "wound" (the continuity of the whole skin is broken) or "gbh" - grevious bodily hard, grevious meaning "really serious", can give rise to either a max of five years, or life. For unlawful wounding the jury needs to be satisfied that chummy did it, and that it was no accident. For wounding with intent, they need to be sure that chummy actually intended to do really serious harm to his victim. Verbals like, "Come here, and I'll kill you!" help, but a lot of it is going to be body language, and inference - did he bring a knife with him (looks more like intent) or did he snatch a steak knife off the table?
With rape, if the victim says "No! You are not for it! I'm a virgin and intend to remain one until my wedding night!" there is no room for the accused to have any belief that she consents. But remember that in English law, unlike French (viol) or German (Vergewaltigung) law, the victim does NOT have to resist. She merely needs not to consent. Of course, there is post-coital non-consent, when she hears the husband's/father's key in the lock, which gives rise to problems for both sides.
If there is violence, then it looks like he knew she wasn't consenting, or simply didn't bother, but if there is no actual violence, and she doesn't resist, it is (usually) just the two of them with no other witness to the actual deed. So, inevitably, it is a matter of what he might have believed. If the jury, having heard his evidence - if he says consent, then he has n o option but to give evidence and submit to cross-examination - retires and after debate, concludes that although not very likely (nice girl from good family!!) she might have allowed him to believe that she was consenting, then they have to acquit.