The first important thing to realize about Blade Runner is that it is a science fiction film (or "speculative fiction", or if you prefer that hideous neologism "sci-fi"; well, how about just SF). What most SF works seem not to realize is that a story probably should not be told as SF unless it needs to be. Unlike Star Wars, which isn't much more than a western shoot-em-up with ray-guns and rocket-ships, Blade Runner tells a story that could only be told as SF. This is because it is the SF elements of the film which are the focus of the story, and director Ridley Scott uses these elements to explore the wavering boundary between the real and the artificial.
This boundary is examined--in true science-fictional form--by extrapolation. With genetic engineering producing replicants which are identical to human beings in all respects except their lack of pre-defined emotional responses and superior physical strength (and perhaps intelligence), this boundary has become a fine line indeed. Scott, and by extension Philip K. Dick who wrote the novel Do Androids Dream of Electric Sheep on which the movie is based, forces us to ask ourselves just what "real" is (a common theme of Dick's work). The replicants are of course man-made, but does this mean they should be afforded fewer rights than "real" human beings? Is this not just another form of discrimination based on characteristics beyond the person's ability (or even desire to) control? Scott goes to great lengths to explore this question by introducing characters who do not know at first that they are replicant (Rachael) and also suggesting that even Deckard might also be a replicant. Deckard would probably have to reevaluate his feelings for replicants deserving full status as human beings and also his role in withholding those rights if he were to one day find out that he was indeed one of them. Which leads to the question of exactly who the "real" people of this world are: emotionless, robot-like (presumed) humans like Deckard, or a replicant like Roy who, despite his inexperience of dealing with emotions and his occasional "questionable actions", ultimately understands the value of life, natural or artificial. However blasphemous, how many of us could not empathize with Roy when he meets his creator and expresses his most basic desire (again, with a skewed emotional response): "I want more life, fucker!"?
Replicants are, in this film, creations of human beings, artificial intelligences to use the "sci-fi" cliché. Some might argue that human beings are also the creation of another Creator, whil others would say we are the natural products of evolution. Neither of these views, however, would really change who we are as people if confirmed, at least on an individual level. Replicants too would probably feel that their ultimate origins do not matter much as far as their status as livings beings, just like us.