in Errand of mercy, I got that the writers were trying to show that Kor wasnt totally 100% evil, by him not just killing spock outright, but when he's an enemy alien, who was caught there when the klingons annexed the world, wouldnt it have been safer, and still seem reasonably civilized, to simply hold him 3 or 4 days till an unarmed transport is scheduled to go to neutral territory, then dump him on some neutral space station.
thats stills howing hes not totally 100% evil.
What unarmed transport going into neutral territory? Certainly not a Klingon transport, they wouldn't bother with that. How many visitors did Organia get? Not many, by the looks of it. And what woukd they be transporting? Tourists? Supplies they didn't need? Landscape services?
Execution, however, I could buy to get rid of a potential enemy. Deportation wasn't the Klingon's style. Why would they do a Vulcan, or anyone, a favor by giving them a ride out of the invasion area? Subjugation and execution was the name of the Klingon's game.
As for not showing Kor to be totally evil, killing Spock wouldn't have done much for his rep in either direction since he killed 200 Organians. Fine, they didn't actually die, but that was his intent. He was a brutal despot. He just happened to be intelligent and personable when necessary, But he was an evil bastard, make no mistake. "You freed two prisoners? Fine, I'll kill 200 hundred of your citizens, and then another 200 every hour" does not make for a sympathetic, friendly character. The charm of the actor made Kor likeable, but his actions were deplorable.