I'm amazed this thread has gone on as long as it has... and that there's still some interesting debate going on, instead of "but I still think Spock was out of character and wrong" without backing it up.
Clearly, there were some holes in the story. Not to say flaws, but gaps of information that leave ambiguity about the situation.
Blssdwlf outlined the main choices rather well:
blssdwlf said:
Kirk's options could be:
1. Outrun the interference, warn Starfleet
2. Maintain a discreet distance behind the DDM and study it for weakness (ala "Balance of Terror")
3. Attack it head on
4. Outrun it heading towards Rigel and attempt to warn colonists to evacuate
5. Lure the DDM to another area by attracting it with the Enterprise's power nacelles
Questionable rationale
The Commodore felt it necessary to continue the attack on the DDM. Why, when there was clear evidence about the fact that an external attack was pointless due to the "pure neutronium" composition of the DDM? The commodore doesn't explain his rationale, only that Sulu keep firing phasers. Spock looked at the facts--attacking the DDM resulted in a wrecked ship and a dead crew. Phasers and photon torpedoes were ineffective. So, logically it is suicide to continue a direct assault on it. The commodore is emotionally caught up in this affair, unable to explain his rationale, and thus Spock has
every right to relieve him of duty.
The commodore didn't say anything like "Yes, the hull seems impenetrable, but there may be a weakness somewhere that we've not yet found. We've got to keep trying. Running off to warn Starfleet will result in the Rigel colonies being destroyed because the planet killer will get there before any help can arrive. This is a battle situation--we must stand our ground, despite the odds against us."
I think it's ironic that if Commodore Decker hadn't stolen the shuttlecraft for a kamikaze run, nobody on the L-374 scene would've had a clue how to stop the alien machine. No dead Matt Decker, no lights-out for the dreaded planet-eater.
How can you say that? We don't have enough information. There wasn't time for the dialog... if Kirk, Decker and Spock discussed the matter further upon his Kirk's return, they might have come up with something. Decker had the idea in the back of his mind... if he wasn't dead, he'd be able to offer up the idea.
Had Mr. Montgomery managed to escort the commodore all the way to Sickbay, it's possible that Spock would have rescued Kirk, abandoned the Constellation, and escaped with the alien machine still on the loose. And Decker probably would've filed a complaint against Kirk and Spock, leaving all three of them the objects of a board of inquiry after someone had figured out how to stop the machine.
Well that's just madness. Spock had all the right to relieve Decker. He was
irrational and unbalanced, unfit for command. Maybe after cooling down a bit, he could've at least been on hand to discuss the options upon Kirk's return.
Choices not explored
Then there could have been some discussion about other choices. What about launching a probe or shuttlecraft to get sufficient distance away to do the warning while the Enterprise continues the engagement? We don't have enough information... we don't know how far away they'd need to be, nor how close the planet killer was to Rigel. Would there be enough time to warn Starfleet and then catch up to the DDM before destroying Rigel?
Unfortunately, there just wasn't enough time in the episode to allow for more dialog... which is a shame, because it would've made for a more compelling episode. After all, Decker came to the conclusion that hey, if we can't penetrate the hull, I'm going to take a shuttlecraft into that thing. Of course he knew it was suicide. Well, why not load up the shuttle with explosives and remote control it into the planet killer? He could have at least proposed this. He was
unbalanced, so he took matters into his own hands, further supporting Spock's proper action to relieve him of command.
Kirk's decision
Mind you, it wasn't up to Spock to take the ship away and warn Starfleet. He was planning to pick up Captain Kirk who would then make the decision as to what to do next! And when Kirk sees what Decker has done, he realizes that this was a more plausible form of attack, and decides the Constellation will be "the bomb" to do the trick.
Who to commemorate
Decker may have had the right idea, but it was Kirk's quick thinking to use
the right tool for the job. He's the one who should have a commemorative statue in the Rigel capital city, as having saved the day. With Commodore Decker beside him... because Decker helped in this matter. If anything, he kept the DDM busy enough until the Enterprise arrived, delaying its approach to Rigel.
Summary
1. Decker was unable to explain his seemingly illogical dogged pursuit of the DDM--direct assault resulted in a wrecked ship and dead crew--so, Spock had to relieve him of command. As further evidence of his unbalance, he made a suicide run in a shuttle. What more proof is needed? He could've brought up the idea of "bombing it from inside", but he didn't. Unfortunate.
2. There was no matter of Spock being poor or out of character in the episode--he was following his captain's orders. Spock may have iterated the need to get away and warn Starfleet, but it ultimately wasn't his right to choose. Kirk was still in command and he would make the final choice.