So I was thinking about Batman. As is usually the case, this came about because I was thinking about another character, Cassandra Cain. In the comments to this post, Mela (third comment) raises the point that it's interesting that Batman would allow this person (Cass) who had killed into his inner circle, since Huntress hasn't really been afforded the same treatment.
First two thoughts:
One, Cassandra killed as a child, Helena was at least a teenager, or early 20s (I had some trouble following the Wikipedia description). As Kalinara pointed out, children have a different level of comprehension of their actions, compared to adults. Might make a difference, like how there's juvie court.
Two, Helena killed (had the man killed?) for revenge, while Cassandra was only following her father's orders. Again, no idea whether Batman would feel that makes a difference, but it seems like he must have. Irregardless, that's not really where the post is going.
My thought was this: is Batman a big believer in redemption? He sees this girl, who killed someone before she realized what that meant, and wants to make amends, and he encourages that attitude (though hopefully not the death wish that accompanied it). I don't know whether Huntress has ever shown regret for her actions, but if she hadn't that might inhibit the Bat trusting/believing in her. But let's go larger, move outside those two characters.
After all the crap that Harvey Dent pulled as Two-Face, Batman was still willing to trust Harvey and ask him to protect Gotham while Batman went soul-searching (or whatever it was he was doing). Sure, it seems to have blown up in his face -and really, who could have guessed a person's who's frequently nuts would regress? - but that doesn't change the fact Bats gave Dent the opportunity.
Taking that tact, Batman's refusal to kill his arch-foes takes on a new light. It's more than just Batman believing no one has that right, or not wanting anyone (even the loved ones' of someone like Joker) to feel the pain of losing said loved one, or whatever other reason Batman has for choosing not to kill. He prefers to capture the criminals, and have them locked up, because he believes that one of these days, they'll realize what they're doing is wrong, and take steps to correct it. And Batman doesn't want to be the one who stood in the way of that by ending their lives, or in the case of some of his "family", by denying them the chance to aid him in his "mission". And who knows? Maybe it's a nod towards Batman's early years, when he (as I understand it) would sometimes dispense justice with hot lead. He changed; those others can too, they just have to want to change.
The problem is, I'm not sure how well it jibes with the jerk Batman we saw the previous decade or so. The fellow who trusts no one, and harbors secret strategies to defeat everyone (I gotta say, I don't think that's really helped his character in terms of likeability, it got taken too far) doesn't seem like a person who would hand out second chances.