What would happen if your identity became hazy and unclear? What if you were a clone of someone else, for instance? Would you still really be "you"? Would you have an identity distinct from the person you're based on?
Those are the kind of questions the replicants face in Blade Runner. Replicants are beings who have been totally constructed and designed by someone else—there's nothing, really, that's quite their own. Nevertheless, the replicants somehow develop emotions and goals of their own, and they go against the very nature they've been created to possess. The fact that Roy—a replicant who's been created to kill—can refuse to kill one of his own enemies seems to call into question the assumptions of his designers. There's something in him that transcends their plans.
"Most people are other people. Their thoughts are someone else's opinions, their lives a mimicry, their passions a quotation." – Oscar Wilde
"There is that in me—I do not know what it is—but I know it is in me.
[…] Something it swings on more than the earth I swing on,
To it the creation is the friend whose embracing awakes me." – Walt Whitman
Without your memories, you would probably just be swimming in a puddle of your own drool. They're kind of the key to everything: if you literally didn't have a past, you would have no idea how to behave in the present.
This is the problem the replicants face in Blade Runner. Initially, they don't have memories of the past, which makes them emotionally inexperienced—they react weirdly to things—they might sympathize more with an oyster than with a dog, for instance. But the Tyrell Corporation creates Rachael as an experiment, to see if they can make a more balanced replicant. She has fake memories implanted, which cushion her responses to things and make her act relatively normally. So do her "fake" memories make her more "human"?
"Without memory, there is no culture. Without memory there would be no civilization, no society, no future." – Elie Wiesel
"Happiness is good health and a bad memory." – Albert Schweitzer
When discussing the killing of replicants, the blade runners tend to use a euphemism: they're not murdering replicants; they're just "retiring" them. But the replicants fear death just like any natural-born human, and their quest on earth is a quest to extend their lifespans beyond the four-year limit they've been assigned.
It turns out to be an impossible quest. Mortality is inescapable in Blade Runner—and if you're not watching the original, happy-ending version, it still hangs over the film's conclusion. Rachael is slated to die four years after her inception, and thus she has a pretty short amount of time to spend with her possibly human lover, Deckard. Then again, Deckard might have a short amount of time left, as well—so they could be evenly matched. But is that much better?
"Death is very likely the single best invention of Life. It is Life's change agent. It clears out the old to make way for the new." – Steve Jobs
"[…] Not to be here,
Not to be anywhere
And soon; nothing more terrible, nothing more true." – Philip Larkin
In Blade Runner, American society seems to be in a state of chaos.
For one thing, it's run by a gigantic and nasty company, the Tyrell Corporation, which creates replicants for the purpose of slave labor. On top of that, even though this society is technologically advanced, it seems to consist mainly of a vast and grimy underworld, where different groups are all participating in a dog-eat-dog fight for survival. It's multicultural, but not in an equitable way—people don't really have the freedom to participate in their society's governance (since its dominated by a corporation), and they seem to have been left adrift at the bottom of the food chain.
"There is no such thing as society. There are only individual men and women." – Margaret Thatcher
"Society does not consist of individuals, but expresses the sum of interrelations, the relations within which these individuals stand." – Karl Marx
In Blade Runner, the world is totally dominated by technology. Some of it is kind of cool—flying cars, people—but most of it is pretty bleak. For one thing, almost all animals have gone extinct, so anything you see, like Tyrell's owl or Zhora's snake, is just a replicant.
And then, of course, there are the human replicants, surely the most dubious technological project in this movie's world. Hey, creating a race of artificial humans to function as slave labor doesn't exactly sound like an idea Gandhi might have endorsed, does it? It goes to show how far technology has advanced in this world. People haven't just used it to dominate and ruin the environment they live in; they've also used it to play God and create Franken-humans.
"Men have become the tools of their tools." – Henry David Thoreau
"All the elements whose aid man calls in, will sometimes become his masters, especially those of most subtle force. Shall he, then, renounce steam, fire, and electricity, or, shall he learn to deal with them? The rule for this whole class of agencies is, — all plus is good; only put it in the right place." – Ralph Waldo Emerson