The
Horta, Medusans, Tholians, Excalbians, and many others would quibble with this characterization.
Star Trek presented lots of examples of treating other sentient creatures, even decidedly non-humanoid ones, with compassion and understanding.
It's also worth pointing out that both
Star Trek and
Doctor Who almost always presented violence as a last resort. It wasn't as if no other ways to conceptualize fantastic adventures existed when
KotB was published.
Now, you could argue that D&D, at least early D&D and particularly Gygaxian D&D, was the product of alternative traditions, leaning more strongly on the blood-soaked adventures of swords-and-sorcery rather than intellectual sci-fi. But even Conan didn't go around slaughtering women and children.
And as for Orcs presented as the always-evil creatures they seem to be in Tolkien's published works, it's unclear whether Orc women or children even exist. They're never shown AFAIK, and no groups of helpless Orcs waiting to be killed by stalwart adventurers are ever encountered.
In fact, upon reflection, the whole "nits make lice" go-ahead to murder helpless non-humanoids in fantasy adventures seems to be novel to D&D. Are there literary precedents for the situations presented in
KotB, implicitly encouraging the slaughter of entire communities of sentient creatures?