And yes, I know that vampires don't NEED to kill when they feed, but that's the nature of the beast. A vampire rises with the desperate need for blood and chows down on the first human it can find, draining them dry. And once they have the taste for it, what actually is there to tell them that they don't need to kill? They don't have souls or a conscience to tell them otherwise, if they have a sire who hangs around and waits for them, they're not going to say 'well, actually, you don't need to kill the guy, just take a few pints and we'll drop him off at the hospital. And if they don't have a sire, then they are literally on their own with no one to explain anything.
And so Buffy stops them before they get the chance.
I mean I completely agree with you, and I understand that ultimately it's safer for everyone if she kills them before they have the chance to do what they're compelled to do.
BUT the issues I have are, first of all, that morally speaking the notion of taking a life in order to punish or prevent something the victim literally
has not done is very problematic and is for me something that's hard to ignore.
Then, to add to the questionable ethics, canon actually tells us that that some vampires, (the two vampires with whom Buffy herself has intimate relations), are sometimes harmless. Now of course the vamps had to first emerge as evil fledglings in order to experience that which made them so, (capture and chipping, Gypsy spell). But what if that wasn't the case? For all Buffy knows, there is a group out there, similar to the Initiative, who's discovered that a far more effective alternative to having to capture a vampire before chipping it is to instead acquire a dead body presumed to have been bitten by a vampire and chip it BEFORE it rises. Meaning that upon breaking ground, that vampire can't harm a soul no matter how much it wants to. And that's just one example. What if a vampire rises with some sort of deformity and can't bite? For all we know, it happens all the time.
I totally understand that where Buffy is concerned, preemptively killing these vamps is not only her calling but actually the most sound form of protecting the living. So maybe, as it stands, she has no choice. But I'd like to see her question it. I'd like to see her do some research, (Giles too for that matter), to ensure that there wouldn't be some reason for which more than 2 vampires are harmless. Most importantly, I'd like the show to have addressed this issue via the scoobies; maybe Willow tries to work on some sort of spell that guarantees that a body won't become a vampire. Or maybe she drives that new chipping plan I described above. I guess the bottom line for me is: let's talk about it a little, you know?