My impression of the story of Oedipus, at least at this point, is that the man starts the play in a situation of immense pressure, and that makes his demise is circumstantially inevitable. As a benevolent king, he cares about his people, and takes it upon himself to solve their problems. It would make some sense, then, that at least one of the issues that would surface down the road would be the death of his predecessor on the throne. After that, it’s all downhill…
In many ways, he’s a victim of the expectations he’s set for himself. When your debut involves sending a riddle-loving monster to Hades without lifting a finger, people are going to put stock in what you say even without the office of absolute monarch. I’m not sure whether to argue for fate here; Greek drama favors influences beyond the sphere of human influence (either through all-powerful fate or godly intervention), but I personally don’t, and the text is deeply rooted in the ambiguity of fate and free will. Oedipus is offered at least three solid outs: first by Kreon asking if he would like to discuss the oracle’s prediction in private, then Teiresias’ obstinacy, and finally Jocasta’s attempt to cool him off after she puts things together just ahead of him. I wouldn’t count the shepherd, because Oedipus is monomaniacally committed enough at that point to use violence to find the answer he’s looking for; still, both Teiresias and Jocasta know what situation they’re objecting to, and so does the audience. Oedipus has a few reasonable points on the side of letting things be, but he doesn’t (well, really can’t) take them. Fate or not, his position dooms him.
In Professor Crawford’s lecture earlier today, he brought up the point that there is a negative side to enlightenment, which Oedipus personally experiences at the catharsis. He experiences this because he finds the truth. He finds the truth, more or less, because he’s got a fair bit of brainpower and an at least equivalent amount of arrogance, essentially situational tunnel vision. Thebes seems to have a bad run with stupid monarchs (Pentheus from The Bacchae has his head so far in the sand he hears the ocean in surround sound), but Oedipus counterbalances his foolishness with the drive and intellect to actually follow through on proposals, which are made as if to a god. Assuming the oracle is an accurate source of information, some ill of Thebes, plague or not, would be blamed on Laios’ death and the apparent stain that left on the city’s fate, and the limping king would have to play detective. Refuse, and fail as a monarch (although it’s doubtful that his pride would even allow the option); follow through, and lose everything. Oedipus dug his own grave well before the start of the play, and by the end, he’s ready to jump in.