So. The major reason that the “Deckard is a Replicant” matter confuses many fans of the movie is that much of Blade Runner is told by implication.
Firstly, Nexus replicants are identical to humans in every regard, including genetics. That’s why the empathy test is required.
Secondly, if replicants live long enough they also develop “emotional responses” IE empathy. That’s why Tyrell corp limits them to five years.
Thirdly, there are millions or billions of replicants in the off world colonies. Every human is given one or more replicants, and Earth has been emptied because so many have left.
So the Replicants are a slave race who are “more human than human”. There’s an endless genocide of human children (all Replicants are under 5 years old), and every human on earth is guilty by implication.
So when Roy Batty kills Tyrell, he’s killing the man who bred and enslaved an entire race for profit. And yet we tend to side with Tyrell in that moment. Even though Roy is clearly fighting for freedom, and trying to save the people he loves.
But because this is all implied not explicitly stated many people don’t think it through.
This is why Blade Runner tests the empathy of the audience. People can have all the information that they are watching enslaved humans being murdered by a policeman. But all it takes is to be told that he “only retires Replicants” and many people completely detach empathy and accept that Deckard is just doing his job.
It’s notable that, even though it’s implicit that Replicants are identical to humans, many people assume they are robots, or have metal parts etc, simply because of the label Replicant. This is exactly how psychological Othering works. Many people only need to have a label attached to a person, and they will de-humanize them in their imagination.
Blade Runner is an empathy test…watch on YouTube…