SHARK said:
What does this impact upon? Well, the occasional non-evil humanoid not withstanding, the majority of all of the young Hobgoblin "children" spared everywhere, by adventurers that encounter them all across the continents of whatever world, (supposing yours, mine, or someone else's,)--will still grow up, if they survive without the parents that the adventurers just killed, (and now the young Hobgoblins will nurse a burning hatred of all humans, elves, and so on who killed their parents and family)--evil, wicked, and depraved. They will grow and prosper, and make war on the humans elves, and so on, like their ancestors before them. Thus, the action of sparing them, will give fruit to further slaughter of creatures that we *know* are good and righteous. I'm still not sure where the payoff is for permitting such a violent, hateful race as evil humanoids to continue to thrive and prosper.
I'm sorry, but I can't let this self-serving circular reasoning go unchallenged.
You agree that while the majority of humanoids are evil, there is a minority that are not.
Yet you persist in assuming... nay, CONDEMNING... the ones that are freed to be mired in evil.
You even fill in the reasoning for them - that they will harbor a burning hatred to all 'good' races.
Why necessarily would humanoids who didn't act evil
- that's why they were spared in the first place - be assured in turning evil?
If the adventurers do something more than just let them fend for themselves, maybe they could do something to change that outcome.
Something akin to, but not limited to "We've spared your lives because you look to not be aggressive and of criminal intent the way the other humanoids were -
Go and continue to do so, and your lives will not meet a grim end, as the evidence before your very eyes I'm sure has taught you well..."
Now to take this approach, unfortunately for your parties, SHARK

would require that the PC's be on the moral high ground.
They can't go traipsing into the humanoids den and just slaughter them because they're 'evil'.
Presumably, the humanoids would have been the aggressors, and the cause of their own demise.
If not, than the PC's really should just stop pretending and realize that they ARE the evil ones in that situation, who have brought death not only to the humanoids, but to their initially-innocent offspring, as well.