One question - please take into account that I am not suggesting with this question that I believe Deckard is a replicant, athough it may sound like it.
Why does everyone who drags out the whole 'The screenwriter and Harrison Ford deny it and Ridley didn't start saying it until later' argument ignore the fact that in the actual shooting script and at least some versions of the screenplay Deckard was clearly and specifically a replicant? There were lines about it in the script. Harrison Ford and Ridley Scott actually fought about it during filming...all of this is documented. Also it is an argument that presents itself as ignorant of the fact that there were 3 screenwriters who worked on it at different times. Regardless of whether Deckard is intended to be a replicant or not, this particular argument is ignorant at best, and disingenuous at worst.
This argument of Deckard's humanity having a definitive answer is tired and pointless...the reason the film is as good as it is is in part due to the ambiguity of this very question. DADoES and Blade Runner both explore the concept of an android that does not in fact know it is an android quite thoroughly, which is what makes this particular ambiguity important to the film. "Questions are interesting, answers are boring."
I would much rather talk about what is uniquely beautiful about the film IF Deckard is human, and then talk about how that changes IF Deckard is a replicant and what that means in order to actually examine the real beauty of the film as a work of art...rather than a bunch of chest beating neanderthalic yelling about who's got the better source for their argument and thumping about how they're right and the other group is dumb and somehow ruining the movie by having a favored opinion.
Watching people have this argument is like sitting in an audience during a performance of Waiting for Godot and having no-one around you understand why it's a comedy.