Re: Dear Doctor... How could you do this?
If the plan had gone the way it was supposed to have gone, the civilization would have been saved and its development would not have been otherwise altered (okay, I suppose well down the line someone might realize the volcano had been tampered with once upon a time...).
Kirk -did- change the civilization. Whatever they will become will not be what they would have become had Kirk not acted to save Spock. I don't think the fact that the entire course of a society was changed should be reduced to "Well they would have died otherwise..."
Indeed, I'd be curious to see the original discussion that led to the implementation of Spock's plan to begin with.
It was the best of Trek, it was the worst of Trek...
"If I lean over, I leave myself open to wedgies, wet willies, or even the dreaded Rear Admiral!"