Really, what's so great about humans? Or rather, why are we so caught up in trying to distinguish between human and non-human? In Blade Runner, we are presented with just this dilemma. Deckard falls in love with a woman who is like any other woman, except for the slight little issue that she is not actually human. She was never born, she didn't have a childhood, she didn't have parents. She has memories, but she never had experiences.
But really, what's the difference? What is it that makes a person who has had experiences that much different than a humanoid creature who looks pretty much human and acts human and is indistinguishable from a human (other than a slight variation in eye movement when responding to a set series of questions)? Perhaps it is that regardless of what memories both individuals may have (or believe that they have), one of them actually experienced an event which is stored in those memories whereas the other one never did. Does a true memory a human make? human.
Perhaps it is just the sentient nature of humans which does not allow us to accept the fact that there are beings that can act and think as rationally (or irrationally, as the case may be) as humans, and yet not be human. Humans have been at the top of the food chain for so long that it is hard to believe that there could be anything out there that could rival, or even exceed, us in abilities. If, however, there is such a being, then we must remain in control. Call it a defense mechanism.
If these beings are in fact superior to us, we could very well be on our way to extinction. Lay on top of that the fact that we ourselves created the beings that are going to lead to our own demise and the need for distinction between the creator and that which has been created becomes more apparent. When we can no longer distinguish what is human and what is not, then being human is not that special any more.