Phew, thread exploded a bit. I'm still lagging behind, so, I'm probably ninja'd, but, I did want to address this.
I agree that races (and worlds) in Sci-Fi are often too homogeneous.
I disagree though on orcs, depending on campaign assumptions. They're a race created by a god that was pissed at the other gods, their nature is part of who and what they are.
In my campaign orcs are not humans with masks any more than a tiger is an overgrown housecat. They are chaotic, they are evil. Yes there are farmer orcs, but their preference is to do raids to get slaves to do their work. They have to raid on a regular basis because the slaves don't last long and so on.
Where do you draw the line? In the Aliens movies, were the xenomorphs just misunderstood? Is there some poet xenomorph that just wants to write about trees? Do some vampires sparkle in the sun?
So yes, for monster races in my campaign, nature overrides nurture pretty much every time. Orcs are not real, nor are they people. They're orcs.
The xeno morphs were presented as straight up monsters. They don't have a culture or a language. They aren't intelligent, tool using creatures. The only real world analogy we can make is to animals. Smart animals maybe, but, animals nonetheless. Orcs may not be real, but, they are intelligent, tool using, clearly sentient beings with a culture and a history and are presented as such.
Meh. I don't think being humanoid makes orcs human. If xenomorphs (I was thinking Sci-Fi) aren't a good example what about werewolves (when shifted)? Vampires? Ghouls? Harpies? Red Dragons? Beholders? Demons?
I agree. You don't need to be humanoid. But, intelligent, tool using beings with a clear history and culture DOES make them human analogues. Werewolves, vampires, ghouls, harpies, etc, don't have a culture or a history, or, frequently in the case of undead or demons, a choice about being evil. They aren't born, they are cursed. Red dragons aren't depicted as having culture, creating art or stories of their own.
It's the depiction of a culture as evil that is the problem, not the physical description.