Coincidentally, I just got home from a D&D session which included a rape, committed by one of the PCs, against a couple of NPCs. On the other hand, considering that this particular game involves at least two cannibals as player characters, the NPCs got off lucky. But then, it’s an evil campaign. It’s also got the highest player mortality rate of any campaign I’ve ever played, almost always at the hands of another player. After all, PCs have the best loot, and if one character is down to his last ten hit points after a particularly tough battle…
But that’s really the exception to how we usually role play, and the entire point of it is to be as over-the-top outrageously evil as possible. In a normal campaign? I dunno. In your average hack’n’slash dungeon-delving type adventure, I’d say it’s out of place. In that sort of campaign, I don’t think you could include it without trivializing it. For something that’s more role playing centric (as opposed to roll playing), particularly something that’s as dark as your average White Wolf campaign setting, I think you’ve got to go in expecting that horrible things are going to happen to your character, up to and including rape. If you, as a player, have a particular problem with that happening in a game (which is an entirely reasonable reaction) I think the onus is on you to make that clear up front, and the GM should respect that. But there are a lot of dramatic possibilities inherent to the situation that could be mined to good effect.
Here’s a somewhat similar example, that doesn’t use rape per se, but a similarly emotionally charged situation. I was recently involved in a one-shot adventure using the Bizenghast RPG. The session was explicitly advertised as a very dark with adult themes. The basic setup is that the players are semi-angelic beings, pretending to be human beings, whose task is to hunt down ghosts and resolve whatever issue it is that’s preventing them from moving on to the next world. You do this by trapping the ghost, then entering it’s psyche where it replays the event from its life that led to its being unable to move on. In this particular case, the ghost was an Irish captain from the seventeenth century, who was responsible for the massacre of a large group of Protestant settlers. When we transported ourselves into the ghost’s psyche, we found ourselves locked in a barn with about a hundred Protestant settlers, under guard by Catholic soldiers. The settlers and soldiers both were just psychic projections from the mind of the ghost. Basically, the memories of a man who’d been dead for three hundred years. But one of the projections was of a pregnant woman who’d been beaten by one of the soldiers, and was in the process of miscarrying. And one of the players, whose character was the group’s healer, was a new mother. She was clearly uncomfortable with the situation, and she ended up using up a lot of her non-replenishable healing items trying to save the baby’s life, even though she knew, on at least three different levels, that the baby wasn’t real. But the scene was one of the most intense role playing experiences I’ve ever had. She was a first rate player (and, I suspect, had a lot of theatrical experience) and she used what she was feeling about the scene to make it into something really transcendent. I think, handled well, a rape scene would have a similar emotionally raw power.
In the examples the OP gave, the first I don’t think is necessarily objectionable. It was a terrible thing to happen to the character, but it sounds like it was played as a terrible thing, and the ramifications (she hunted down her attackers and killed them) were incorporated into the game. I’m guessing (since they were teenagers at the time) that it wasn’t incorporated into the game very well, and probably came off as exploitative, but I think that’s more a function of the gamers’ ages as the subject matter. In a mature group, it could be a powerful storytelling tool. I don’t necessarily know how I feel about the idea of springing it on the player without warning. It is an emotionally charged subject, and I can understand why a player might not want to go there. On the other hand, having to deal with it when you don’t want to deal with it has a narrative power itself. Certainly, the character doesn’t want to have to deal with being raped, and putting the player in that same situation could make the player’s response more real and immediate.
The second example is simply crap GMing. The GM should never take control of a character away from a player. Even when the character is under the control of someone else, that control should be presented as a role playing challenge to the player. If you’re a paladin who’s under the mental domination of a wizard and being forced to attack the rest of the party, the player should still be controlling the character, but making his decisions within the strictures imposed by the GM. In this particular case, the GM should have said something along the lines of, “The potion makes you feel better. A LOT better. In fact, you’re feeling kind of horny and uninhibited… and Player B looks pretty hot right now.” And not giving Player B any input into what happened between the two characters is inexcusable, as that character wasn’t even under the influence of the potion.
On the subject of rapists as PCs, that’s a bit tougher. In some campaigns, such as the one I described in my first paragraph, it can work, because the entire thing is a Grand Guignol showcase of the absurdly degraded. But in that sort of campaign, you pretty much forced to keep a lot of emotional distance between you and your character, just because of the sort of abominable monsters the campaign calls for. In another sort of campaign… well, I guess I can see it working if one of the characters is meant to be a mole for the GM, who at some point in the story is meant to be exposed as a villain and then used as a foil for the PCs from then on. But even then, I’d only go there with NPCs as the victim. Having a PC rape another PC would, I think, ultimately poison the group dynamic beyond repair, certainly for that campaign, possibly permanently. Even in really good groups, there’s always a certain amount of power struggle between the PCs, and throwing rape into that mix is going to fuck that up completely. Even if the player doesn’t have a particularly strong emotional reaction to the concept of rape itself, allowing his character to be put in such a helpless position in relation to another player is not going to end well. I’d only allow it if both players agreed to it before hand and were really interested in exploring the ramifications of the rape, and how that would affect their characters interactions. And, of course, there’d have to be some sort of plausible excuse for those characters to interact in any way that didn’t involve heavy artillery or advanced cutlery, unless the ultimate goal of the set-up is for one of the players to kill their character off permanently.