I decided to stop messing around and go straight to the source. Excerpted below are some quotes from an interview of Ridley Scott, conducted by Danny Peary, which appeared in the book OMNI’s Screen Flights, Screen Fantasies (1984). This volume is chock-full of interesting interviews and essays and I recommend it heartily, if you can find it. Anyhoo:
Peary: Except for the fact that he tracks down renegade replicants rather than standard criminals, our hero Deckard is in many ways like the classic disillusioned, morally ambivalent detective - which is fitting considering the other noir elements found in the film, including his hard-edged narration.
Scott: When we first meet Deckard, he is already thinking of giving up his job as professional exterminator. The job was in fact getting to him, as it did to, say, Philip Marlowe…what I wanted to do at the beginning was show a man who wanted to change his whole way of life and was in a way trying to find some kind of absolution or, maybe, a conscience…The scene [in which Deckard kills Zhora] ends with Deckard looking down at this “woman” he has just killed and we get one more facet of the reason he wants to quit his profession. For we’re now dealing with a man who is guilt-ridden.
At this point, it seems clear to me that Scott planned Deckard to be burnt-out, emotionally wasted, seeking redemption, but definitely human. But then he takes a short hop through the Twilight Zone:
Peary: In the novel, Deckard constantly worries he will mistakenly kill a human he thinks is a replicant. In fact, he constantly worries that he, himself, is a replicant.
Scott: At one stage, we considered having Deckard turn out to be, ironically, a replicant. In fact, if you look at the film closely, especially the ending, you may get some clues - some by slight innuendo - that Deckard is indeed a replicant. At the end there’s a kind of confirmation that he is - at least that he believes it possible. Within the context of the overall story, whether it’s true or not in the book, having Deckard be a replicant is the only reasonable solution.
Scott want sit both ways, it seems. He could have included scenes that stated unambiguously that Deckard was (or was not) a replicant, but preferred even then to keep it vague. If he planted firm evidence that Deckard was a replicant, he made it too subtle, at least for me. I find the interpretation that Deckard was losing his humanity (though his love for Rachael restores it) while the advanced replicants were gaining theirs to be the most satisfying, on a spiritual and logical level. Some lame-ass plot twist saying Deckard is a replicant ruins a perfectly good film and I choose to ignore it. If this is what Scott intended, he did a piss-poor job getting his message across. Then again, considering the original novel was a hallucinogenic flight of fancy, maybe he did the best he could.