Faith’s outlook isn’t wrong
I disagree with this. The whole point of Faith is as an example of the existential idea of 'bad faith', which is basically 'a refusal to confront facts or choices'. I believe that's what Whedon et al were aiming for, a character who embodied this philosophical view. I understand if that doesn't work for you and the writers missed the mark.
as Faith is not yet at the point where she is advocating murder.
By not accepting what she'd done, by not finding a moral way of dealing with it, she is, in my opinion, advocating murder. She is essentially saying that it's ok to murder people because she has done so much good in the world, and that balances the scales. She is saying that she takes no responsibility for her actions, that she didn't have choice, that the victim was to blame. The way she dealt with the aftermath of Finch's death makes her morally questionable.
Buffy is probably making it worse
Buffy offers Faith help and kindness, which Faith throws back at her. Maybe Buffy was in the wrong, maybe she should have taken a step back and left Faith alone, I could possibly agree with you. But then Faith goes to Giles and blames Buffy for Finch's death and I think that's her lowest point in this whole thing.
Faith talks a good game, how brave she was jumping off a rock into the water when she was a kid, how strong she is wrestling alligators, how she has no time for the little people around her because she's special, but when it really comes to it, she's morally weak, refuses to take responsibility and blames others for her own actions. She is a brilliant metaphor for an existentialist concept and I think she works really well as that.
Then in Choices Buffy honestly has a crappy choice to make and I do cut her slack I’ve even admitted that I would probably do the same thing while at least recognizing that my choice would be morally questionable. She definitely is passing judgment on Wes when she ask him if he even has a soul. When Giles makes a similar suggestion with Dawn she’s angry with Giles and she never admits it but she does know on some level she’s selfish. By taking the stance that she’s the Slayer and that she therefore has the right to make the choice that Willow’s life matters more that everyone else’s then yes she is contradicting herself.
Buffy is consistent in both cases. The watchers want Willow and Dawn to die for the greater good and Buffy says she will rescue/save them. I have a hard time thinking of her as selfish, because she sacrificed her life to save the world. But I do see how it could be read as that.
She can’t be right in both cases while different situations her words actions contradict each other. She either does have the right as the Slayer to decide that some lives matter more than others or she doesn’t it can’t be both.
I think you're probably right here. We don't see the full embracing of this until Season 7, when Buffy declares herself
'the law', but I think each season is a step on the way to her understanding that this is who she has to become.