Possible spoilers.
Let's rephrase the question.
Would killing a line of mosquitos be evil? Probably not, or we have some wicked, wicked exterminators in the real world.
Would killing a whole horde of illithid be evil? Aberrant, brain-sucking monsters? What if one of them was a vegetarian (ate the brains of Treants, maybe)? I suspect a LOT more people would say "not evil."
Miko, the pala-monk of questionable sanity, was perfectly fine with slaying the baby dragon because "its scales weren't all shiny." Roy had a run-in in the prequel books with a "good" party that was perfectly fine slaughtering orcs who were just waiting in line for concert tickets.
In the real world, up until relatively recently, you were considered good if you killed other humans who weren't of your tribe/religion/ethnicity/book club.
The only "correct" answer is that V's acts are evil if Rich Burlew defines them as such, since he is in fact the Dungeon Master of his world. Any other answer is arguable.
Whether certain cultures and the gods that support them judge something as evil or not does not translate to whether it is evil by our morality, or even by the generic D&D morality.