My views:
1 - it is almost always relevant whether the alleged victim has had consensual sex with the alleged rapist before. My understanding is that most laws recognize this.
2 - I would find it extremely relevant as a juror or judge if the victim had not merely never consented to sex before, but had done so in deliberate fashion. That is, it wouldn't be helpful to me to know that the alleged victim was still a virgin just because the right man (or woman) had not yet appeared on the horizon. But it would be helpful to me to know that the alleged victim had openly vowed to be a virgin forever, until marriage, or until some defined event in the future that had not yet occurred (e.g. first serious relationship, even.) If the prosecution can demonstrate that the alleged victim would not have given consent to ANYONE, then obviously it is more likely that she would not have given consent to the alleged rapist. My understanding is that most laws do NOT agree that this evidence should normally be admitted.
3 - For all other women, I agree with blocking evidence of past sexual activity with people other than the defendant, but I feel conflicted, as described below. Whether someone has consented to sex with 1 person, 3 people, 15 people, or 63 people honestly is not very helpful to me to know whether she would consent to sex with the 2nd, 4th, 16th, or 64th. Or, put differently...
I guess that someone who has consented to sex with 63 different people may be more likely to consent to sex with a generic 64th than someone who has consented to sex with only one person (e.g. her husband of 25 years.) But there are any number of reasons that our...sexually successful...woman with 63 partners may have chosen not to consent to the defendant on the day in question. She may not have found him sexually attractive. She may not have been in the mood that night. She may have known something about him - e.g. a dread STD - that made him unappealing as a sexual partner. She may recently have quietly decided (i.e. no dramatic religious conversion that she can introduce into evidence) to give up her...active lifestyle. What troubles me is the extremely (unfairly) prejudicial nature of the evidence here - without fail, the defense attorney is going to stand up, point at the alleged victim, and say: "Ladies and gentlemen of the jury, the *sneer* so-called 'victim' here had had 63 sexual partners. Sixty-three! If you started today, that's like having a different sexual partner every day for the next nine weeks! Now, I ask you, do you think that a...person like this got raped, or do you think she consented to sex?"
In most parts of the United States, or of the world, how do you think a jury is going to answer that question? "If she was having all that sex, okay, she probably consented this time too." The result it seems to lead to is, once a woman's sexual activity reaches a certain level, she can't ever successfully allege rape. That she had sixty-three sexual partners means of necessity, to a jury in a courtroom, that she probably wanted the sixty-fourth.
Now, of course, 64 is a caricature, and applies to fortunately few women. I would say I'm more concerned for women who have had, say, 1-10 nonmarital sexual partners. In many areas of the country, this is still very much frowned upon. I'm concerned for the woman who has had sex with two of her past boyfriends, gets raped by a third person, and the defense attorney in Backwater, USA persuades the jury that because she'd been willing to consent before marriage, then surely she was willing to consent again (what with her being a person of low morals, and all) - and moreover, since she wasn't a virgin, the damage done would have been relatively slight in any case.
So I come down supporting rape shield. But on the other side of the equation is the hypothetical innocent defendant, incorrectly accused by a woman with wrongful motivation. She says they met at a party, he offered her a ride home, then he came upstairs without her permission, forced her inside, etc. He says, here truthfully, that she invited him inside, they shared a meaningful glass of champagne in her living room, and then they retired to the bedroom for... consensual activities of a mature nature.
Should he not be permitted to show that she has previously been intimate with eight other guys under similar circumstances, especially if it's otherwise "he said, she said" and that's the best he's got? It's a hard question.4 - an interesting one that doesn't get discussed as often, but that I've been mulling about with some friends. Should sexual orientation be probative of anything? If someone can demonstrate that she is a committed lesbian who has had ten previous female partners but is adamantly disinterested in having sex with men, should that be introduced to show that she more likely didn't give the guy consent? And what about in the more rare, but still existent situation when a purely heterosexual woman claims sexual assault (or rape, depending on how the jurisdiction defines it) by another woman? Again, it seems to be relevant to show that she didn't give the woman consent. AFAIK, this last one isn't really addressed by rape shield laws (which are mostly to prevent the defendant from claiming that the victim consented by virtue of her sexual history, not the other way around), but it's an interesting collateral question.
