Mindfire
Istar
Again, surely this depends on the mythos behind the vampire. What if the vampire is an infected or possessed human that is driven to kill against it's will? You could kill it, sure, but what if you could cure it instead? Is it morally right to kill a vampire just because it is the easy path? This reminds me of the argument behind whether or not to shut off a coma patient's life support. Well, sort of.
Also, check the story of I Am Legend. He kills the vampires without mercy, under the assumption that they are all violent and evil. The ending of the story reveals that the morality is reversed.
Not entirely. If I remember correctly, there were actually two types of vampires: the mindless killers and those who just wanted to be left alone, and he'd been killing both groups indiscriminately. But his mistake in killing the second group doesn't mean he was wrong to kill the other group.
Regardless, I Am Legend depicts an entirely different scenario from the one I'm referring to. I'm talking about vampires preying on a large group of people, which shifts the morality involved considerably. And even if it is possible to cure them, does that mean you should just let them keep on killing and turning people until the cure is found? That you shouldn't proactively protect your citizens? And what if some of them don't want to be cured, and would rather go on eating the flesh of men for all eternity? Should you just "live and let live"? Of course not.