One of my favorite films is Blade Runner. In part this is because of the film's discussion - unwittingly or not - of "being."* What does it mean to be "human?"
Tied up in that discussion is the question of whether Deckard is a replicant. Personally I think it depends on which version of the film you are seeing. In the original release - which I admittedly haven't seen in years - he probably isn't a replicant. Or at least the evidence for such isn't particularly strong. However, in the "Director's Cut," with its use of the unicorn as a way to tip off the audience, he quite clearly is a replicant.
Addendum I: It is fairly clear from the novel on which the movie was based that Deckard is a human; he is a human who cares about these replicants, that is one who empathizes with them. Empathy - as Adam Smith noted so long ago - is one of the core aspects of human sociability. If a human can empathize with a replicant, does that make the replicant human?
Addendum II: By the way, Deckard's rationale for killing replicants (in the novel) is in order buy a "real animal" - that eventually sets up a real bit of irony. Anyway, by this time in the Earth's history "real animals" are fairly rare and they are something of a status symbol. All Deckard has is an electric sheep, whose "real nature" he tries desperately to keep hidden from his neighbors. A little bit of this part of the story bleeds into movie vis a vis the snake scale that Deckard tracks down. Anyway, Deckard ends buying a real animal - an Emu or an Ostrich or something like that - while also taking in Rachel (a replicant). He loves Rachel and decides to tell her what she is; her reaction is to kill the Emu.
*Click here for some nice quotes on "being."