I jump around games quite a bit, so I haven't finished RDR, but I will point out that I don't see why so many people act like that achievement is a big deal. I think the way most people go about it says more than the achievement itself and it's existance.
To put things into perspective, as many people point out pretty much all the women that you meet outside of towns are honey traps out to rob you, kill you, or both. There is no reason why you need to abduct a nun, a prostitute, or some innocent lady, and then murder her with a train.
Me? I got one of those encounters where the lady yells "help" near a wagon and then you get ambushed (including her going red). I just shot the dues, lassoed her, and engaged in a bit of frontier justice with the train. I mean she did try and kill "me" after all, right? I otherwise would have just shot her. There is no real bounty for turning in these general interlopers either, so it's not like you can put them in jail or whatever.
I suppose you can say it's a bit brutal, but hey, in that encounter she was the ringleader apparently.
You've also got the ladies who try and steal your horse, I've never used one of those, but again horse theft is a death penelty offense.
All told RDR is a good game, not sure if I agree with the role-playing arguements for the most part though. As I've said before what makes an RPG is the use of stats to resolve problems rather than the player's own abillities, and even if not the most difficult game out there, RDR is definatly an action game, that depends on the player's reaction time and abillities. I typically make the point that they very first RPGs had absolutly no plot or anything else, the appeal being mostly to wargamers who took nerd-like joy in having been able to create statistical engines to simulate individual battles rather than larger scale engagements. Adding plots and storylines and such came later, maybe not a lot later, but still down the pipe. Unless RDR goes stat based, it will never be an RPG unless you try and re-define what that is all about, since RPG in thise case does not use the term "role playing" in the sense of an actor playing a role or whatever, but in the terms that it's the abillity of the role/character to resolve events rather than that of the player.