Well, this is interesting, so I'll write too much and bore everybody.
To be honest, I don’t like to extrapolate too much about Kirika’s past just as I don’t feel completely comfortable attesting to Altena’s, or even Chole’s, motivations. Some things are, of course, assumable: Kirika was shown/taught at a young age that murder, for her anyway, was normal, if not just okay. How much of her acquiescence came from a desire to please isn’t confirmable, even if likely, and I’m hesitant to ascribe the chibi Kirika with the wherewithal to consciously be seeking love, though I think that on an unconscious level it’s quite probable. As for hatred? Like the fat Italian, I think her hatred is really for herself; otherwise, she’d have little reason for disassociating so completely parts of herself. Perhaps this is the hatred that saves Kirika: it saves her from herself? Nah, that doesn’t seem right, either.
While the structure of Noir is the basic hero’s journey (Kirika’s search for her lost self), I think much of Noir can be viewed as a traditional Western revenge plot: at least for Mireille, the cause is not simply the search for a truth but for the possibility of enacting vengeance for her family’s murder. The revenge plot is very similar to the hero’s journey (in fact, here it parallels it), except that the quest is not to gain anything, but to force someone else to lose. It stems from a belief, for the wronged party, that violence can provide restitution, that destruction can offer retribution, that vengeance can lead to salvation; in short, that hatred can save.
I think perhaps, in the larger picture, you could assume that Altena’s ideal of hatred saving, in the context of the Grand Retour, is itself a massive scale revenge plot. We see enough of her childhood to know it wasn’t pleasant, and if her wish is to revive a Noir to protect the peace of the newly-born as she herself wasn’t (I do think this is her main motive) then, with her past experience in the forefront of her thoughts, it’s also possible that part of her motivation is to revive a Noir to seek vengeance on a dark and corrupt world for its evils: evils that include those perpetuated upon her. Who else to blame for this evil than the Soldats, who are the world, themselves. Altena admits as much toward the end of the series. So the character who espouses the “hatred can save” philosophy is herself constructing her own revenge plot. Her hatred, through the Grand Retour, may “save” the Soldats of old, and conversely, the world itself. Now, whether this thinking means that Altena prefers the vengeful Mireille as a part of her Noir is pretty debatable: given Japanese preferences for open- ended storytelling, I think you can make the case either way convincingly. Of course, Altena is such a whack job that attempting to reconstruct her motivations is a pretty slippery slope anyway.

As for poor Chloe, so much of her philosophy parrots Altena it’s hard to say just what her motivations are. Did she have love? Of course. Did it kill her? You could say that if you wished; either her love for Kirika or, with a certain interpretation, her love for Altena led to her demise. One thing is for certain: hatred did not save her, and if anything, her attempted revenge certainly had her killed.
But then, as the series tries to communicate, hatred never saves. Odette offers Kirika the morsel that brings her out of her indecision: “Love can sometimes kill, but hatred can never, ever, save.” Once Kirika remembers that declaration, her choices are pretty much set, her rejection of Noir, of the vengeance plan, is the path her journey is now set on. But she is not the character that embodies this rejection the best.
Which of the four characters represents this idea the best? Ironically, it’s the vengeance driven, hate mongering one with a righteous mission: Odette’s daughter. Why? Because she is the only one, after all, who ever actually forgives. She forgives Kirika, and that forgiveness for her family’s destruction is not only remarkable, it is the clearest example of someone being saved. If anyone is saved, it’s Kirika, from Mireille’s bullet, from her dark self, and from a fiery pit. Each time, she is saved by love.
Of course, you can make the argument that Mireille is saved by Kirika’s love, many times, through out the series, but Mireille’s salvation through love is less remarkable to me than her rejection of hate. Her seemingly sole motivation throughout the series has been acting in anger, single-mindedly searching for vengeance, taking it where she can find it (the Soldat in the church in ep 5 comes to mind). That’s what makes her refusal to shoot Altena so remarkable in the end. She, without being told, embraces the beliefs of her mother: she understands that hatred, revenge, will not be the thing that saves her in the end.
One could also argue that when Mireille finally completely abandons her revenge plot, she shows Kirika the way to come to the end of her journey and find the self that she’s been seeking. I don’t think it is a coincidence that when Kirika mimics Mireille's example, and also refuses to shoot Altena, she is able to name herself, and take on her sins as Kirika, and not Noir. But I think I’ve rambled enough on the subject for now.
Good call, Fellini.