Luke DID see his real father. You know, Anakin, the guy BEHIND the Vader mask?
Everyone likes to cling to Obi-wans line about how Anakin died when he became vader, but why are we listening to ObiWan? It seems obvious from his stance that he doesn't believe Anakin can be redeemed and is therefore dead.
On degobah luke says
"I can't kill my own father"
to which obiwan replies
"Then the emperor has already won"
This seems to imply that obiwan excpects luke to kill vader because Vader is pure evil and cannot be redeemed. But we see differently at the end. Anakin is redeemed, he returns to the lightside and is the good man that he could have been all his life.
Replacing him with Hayden christensen is like saying "no, he really wasn't redeemed, he was still Vader, this is the only Anakin"
And THAT is garbage.