The whole point of the movie, besides the cyberpunk dystopia that it created and popularized, is that Deckard is a HUMAN who acts like a ROBOT. He has no joy, no purpose, no meaning. And he rediscovers all of that, ironically, from his interactions with replicants - Roy Batty and Rachael most of all. It’s the Sarah Connor, end of Terminator 2 thought that “if a machine - a Terminator - can learn the meaning of life, perhaps there’s hope for the rest of us.”

And that DOESN’T FUCKING WORK if Deckard is a replicant. Philip K Dick, Harrison Ford, EVERYONE on the production EXCEPT Ridley Scott either knew this or figured it out. But because Mr. Auteur decided to share his braindead take and even cut a scene from a whole-ass other movie into Blade Runner to make you think MAYBE the robot-killer cop is himself a robot because “whoa man how mind-blowing”, now we have to get people saying that’s how it is for the rest of humanity.

Deckard is not a replicant. END OF.

edit: it has been pointed out to me that Harrison has reversed his stance on whether Deckard is a replicant, and my last sentence was factually incorrect in that there IS, of course, ambiguity in the film about who’s a replicant or not. Making Deckard into one, IMO, is still a braindead take that makes the movie subjectively worse, but I should still try to be accurate.

That’s never explicitly stated in the movie. I believe it’s hinted at just enough to make you wonder. Which in turn makes you wonder what even makes a human person. In the sequel I think they pretty heavily lean on him being human.