On the threatened planet in "One of our Planets is Missing", it takes Governor Wesley about eight seconds to decide that their resources have to be dedicated to evacuating the planet's children above all other considerations, and most of the planetary population accepts this very quickly. Then it turns out to be unnecessary, since the space cloud is a Non-Malicious Monster and, having been made aware that the planet is inhabited, immediately agrees to leave - it only threatened the planet in the first place because it couldn't detect the smaller life forms.
Kirk is adamant from the start that McCoy cannot be guilty, even when the doctor himself questions whether maybe he started the plague by accident.
Spock breaks McCoy out of prison to find a cure for a disease which is killing the Enterprise crew. The Vulcan reminds him that if he goes and fails, he will also die. Bones' response? "I'm a doctor, Spock. A doctor. Get us beamed aboard!" Not since "The Empath" has one of McCoy's reminders about his profession been so heart-meltingly awesome.
As is his joy and relief when he finally gets proof that he didn't inadvertently cause the previous plague.
In "The Pirates of Orion", McCoy's attitude around the terminally ill Spock.
Thelin: True. A warrior race has few sympathies, but one we do possess is for family. In your time plane, you will live and so will your mother. That is valuable. [gives Spock the Vulcan salute] Live long and prosper in your world, Commander Spock.
Spock:[returning the gesture] And you in yours, Commander Thelin.
Behind the scenes, Leonard Nimoy dug his heels on returning to the role of Mr. Spock. Not because of any antipathy to the character, but because Filmation (a notoriously budget-conscious company) didn't want to hire on George Takei, Nichelle Nichols or Walter Koenig note The plan, as far as can be determined, was: hire the three main stars (Shatner, Kelley and Nimoy), and then hire on Majel Barrett and James Doohan to essentially play everyone else save for a very occasional guest star. Nimoy essentially told Filmation "If you don't get Sulu, Uhura and Chekov, you don't get Spock." In the end, Filmation and Nimoy came to a compromise. Takei and Nichols were hired, and Koenig was guaranteed an option on a script for the series, eventually turning in the episode "The Infinite Vulcan".