Who knows what is right? By whose standard? By what culture? In what era? What do we owe each other? Am I my brother's keeper? And so on... The weak do not suffer what they must. They can choose to fight back in their own defense, they suffer by their own choice.
Survival of the fittest is nature's way---it is neither good nor evil. Sometimes you survive by teamwork, other times by acting on your own. The weak can work together to overcome the strong. Then the strongest of the weak becomes the strong.
To say "the orc is violent and savage and must therefore be slaughtered on sight because these things make it evil" is justifying many of the atrocities mankind as perpetrated on ourselves throughout history. If the orc attacks and you must destroy it in your own defense, this is not evil. It is survival of the fittest. You are fitter than the orc. Or are you just evil for doing so?
No culture has the right to destroy another simply because they deem it evil, or that culture is evil itself. The orc conquest and destroys because they do so to survive--for plunder, food, equipment, etc. and their means for destroying is savagery and violence.