To me, the episode makes perfect sense. The creature is an alien, and in this, its sense of ethics and morality could be equally so. It might proceed from the basis that its survival is more important than anything else, and deception and manipulation are appropriate survival strategies. It would then not be trustworthy in negotiation. After all, it certainly could have negotiated through Crater, but it chose not to. It could have proceeded from the standpoint of peace. It chose instead to deceive and manipulate from the very beginning, and it's actions were equally hostile.
Assuming it shares a human sense of ethics and morality would be a mistake. It certainly could have learned what these were from Crater if it didn't already know. Beyond that, it was clearly a danger. Not only could it change form -- or at least manipulate people's perceptions -- but it could also hide from Spock, a telepath. It murdered several crew and stowed away aboard the Enterprise. It then murdered Crater when he was both no longer useful and a potential threat, showing no sign of loyalty or the love that Crater said it needed.
We have no information on why this creature is the last of its kind. For all we know, it destroyed the others. It could well have been a psychopathic criminal among its own. But its will to survive at any cost was its defining quality.
Kirk was correct to treat it as a threat and not as a misunderstood sentient being. It's choices as an intelligent creature were hostile.
Even when its pretending to be McCoy, we don't know that anything it expresses is to be trusted. So what if it says there's no reason to hunt it down -- if we take that sincerely, then its arguing that it wants peace, which we've already seen isn't true. If we take it as a more likely deception, it's merely trying to interfere with the ongoing efforts to locate it. Certainly, if the creature was being sincere at that point, it could have outed itself and surrendered, letting Crater act as a representative for its interests. Instead, it chose to manipulate and later kill Crater, too. It was simply lying.
Assuming it shares a human sense of ethics and morality would be a mistake. It certainly could have learned what these were from Crater if it didn't already know. Beyond that, it was clearly a danger. Not only could it change form -- or at least manipulate people's perceptions -- but it could also hide from Spock, a telepath. It murdered several crew and stowed away aboard the Enterprise. It then murdered Crater when he was both no longer useful and a potential threat, showing no sign of loyalty or the love that Crater said it needed.
We have no information on why this creature is the last of its kind. For all we know, it destroyed the others. It could well have been a psychopathic criminal among its own. But its will to survive at any cost was its defining quality.
Kirk was correct to treat it as a threat and not as a misunderstood sentient being. It's choices as an intelligent creature were hostile.
Even when its pretending to be McCoy, we don't know that anything it expresses is to be trusted. So what if it says there's no reason to hunt it down -- if we take that sincerely, then its arguing that it wants peace, which we've already seen isn't true. If we take it as a more likely deception, it's merely trying to interfere with the ongoing efforts to locate it. Certainly, if the creature was being sincere at that point, it could have outed itself and surrendered, letting Crater act as a representative for its interests. Instead, it chose to manipulate and later kill Crater, too. It was simply lying.