Rush Limborg wrote:
Spock would seem to disagree with you. See his remarks in "Devil In The Dark", when he pointed out to Kirk that, as far as they knew at the time, the "creature" (the Horta) was the last of its kind.
The fact that there was only one salt vampire left, is secondary. The use of the word 'genocide' implies deliberate, malicious intent.
If there is a creature who is trying to kill you, and you kill IT before it can, that is not genocide. It's pure, absolute self defense, which is everyone's right.
If, however, you say "I hate this race and want to wipe it out on general principles" and you do so, THAT is genocide.
To put it another way: If there had been other salt vampires in existence at the end of this episode, McCoy would not have hunted them all down to extinction. He killed this one because it was trying to kill Kirk. End of story.