Leaving Geatano in ememy territory alone with no knowledge of the terrain, in a foggy area with hostile creatures who are proven killers is a good decision on Spock's part?
When Spock orders Geatano to stay behind Geatano and Boma look at each other like "I'm/you're dead." and so he was.
It was the writer's fault, but Spock makes a lot of dumb decisions in the episode.
When the crew complains about Spock not being inspiring--they're not talking about a long-winded "don't fire until you see..../give me liberty or give me death" speeches.
They mean the simple things that Kirk and most commanders do to inspire confidence in a tough situations--gestures, actions, looks, small encouragements.
Not lecturing people who have seen their comrades die and are in iminetent dangerabout "their duties to other life forms"
If his duty to the natives is a component of his decisions--he doesn't need to broadcast it.