How does Oedipus act intelligently or morally with his prophecy of doom in Oedipus Rex?
To which prophecy are you referring? There are no less than 5 oracles of doom in the Oedipus legend.
#1: Oedipus will kill his father and marry his mother.
Intelligent decision: Oedipus flees Corinth, where he thinks his parents live. He doesn't want to harm his family. I wouldn't say this is a moral decision, as he is trying to escape and deny his problems. Inevitably, this leads him to Thebes.
#2: The Riddle of the Sphinx
Intelligent decision: Oedipus solves the riddle and frees Thebes from the plague. This ironically leads to immorality, as he must marry the queen, his mother. Oedipus solves the riddle by answering "Man," but he fails to understand the other half, "Woman," and the riddle's three-part prophecies--that he will suffer on two, three, and four legs.
#3: Laius' killer has plagued Thebes
Intelligent decision: Oedipus investigates the crime, calling forth key witnesses Tieresias, the messenger, and the herdsman. However, he fails to heed their advice, which is to avoid their questioning. He also fails to call forth the key witness Jocasta, until it is too late.
#4: Laius' killer must be exiled
Intelligent and moral decision: this is Oedipus' best and worst moment. He blinds and exiles himself in order to rid the city of his own plague. Though cursed, he finally attains wisdom and becomes a Tieresias-like prophet.
#5: Oedipus proclaims his sons will kill each other
This doesn't seem very intelligent or moral, but it ironically is a way to end the doom, incest, and plague upon the family. Eteocles and Polynices do kill each other outside the gate of Thebes, thereby setting the stage for more female suicide, Antigone's.