I think you're totally off the mark on that one. The movie works both ways, if you take that he's a replicant the story goes that humanity has completely lost its soul and that the children of men, the replicants, are able to attain humanity, despite being synthetic. Deckard starts as just a tool of the humans but by being confronted with the moral ambiguities of his job and the relationship with rachael, comes to reject his predestined fate and chooses his own path... in a sense, rejecting the will of his "parents" and becoming his own person.