Not at all - in fact it was clearly shown in the episode that the only reason Edith Keeler got killed was by distractedly crossing the street to meet up with Kirk - remove those distractions and she would have lived on to initiate that troublesome peace movement (a parallel universe, details of which the Guardian Of Forever helpfully loaded into Spock's tricorder). Spock, Kirk and McCoy were always required to make these events happen, as without McCoy jumping into the past there would be no reason for the others to follow, and without Kirk to woo Edith she wouldn't have been so spaced out as to not cross the street safely!
This is a classic case of a predestination paradox and all the GOF had to do to ensure that it happened was spout a few poetic lines to the landing party and block off their communications to the Enterprise. In fact, I would go so far as to propose that the GOF exists in order to perpetuate predestination paradoxes, which would explain why it seems so free and loose in letting interlopers trespass in past events. Otherwise its not much of a guardian, is it?
By the time of
Yesteryear the GOF is apparently being used for limited time travel related research by a science team, perhaps under the belief that history can be altered otherwise. However, the GOF knows that there is still one more predestination paradox involving Spock that it needs to perpetuate and this time a simple communications blackout won't cut it! Instead, on Kirk and Spock's return journey from ancient Orion the GOF diverts them to a close parallel universe, one where Spock died as a child, an Andorian named Thelin is first office of the Enteprise and NOTHING ELSE HAS CHANGED. I guess Spock wasn't that important after all, eh?
Under the impression that history has changed, Spock again ventures through the GOF to perform his pre-ordained tasks.
