Kirk (TOS) was inconsistent when dealing with 'monsters'. He was happy that Lenore (the killer of his friend and 6 others) was being cared for and he seemed to let Dr Coleman off scott free despite being involved in several deaths and in helping Lester try to kill Kirk.
Yet Kirk didn't even attempt communication with the cloud creature in "Obsession" or the creatures that were attacking Deneva. Perhaps they were misunderstood like the Gorn and the Horta.
I personally give the Salt Vampire killing a pass because they didn't seem to have a choice. Though that was of course the writing. They wanted to show I think McCoy and Spock's loyalty to Kirk I think so the Salt Vampire's death was incidental.