"Prefer" father? you're crazy! That's Roy's (or mankind's, rather) moment of complete anger and frustration with his God. His four years represent the time that never seems enough to any of us! He has killed his way to the answer of his existence, and is thoroughly pissed off that his God saw fit to make him mortal. It is mankind's everlasting anger with his creator.

"All those moments will be lost like tears in the rain"--that's life--that's God--that's why Blade Runner kicks so much ass.