Quote fromWhy is everything always good vs evil? Why do we always get presented with a so-called perfectly good hero, and he always just so happens to have a perfectly evil double? What is with people's obsessions with polar opposites? Why do so many people think in black and white?
What does it even mean to be good? Its obviously a matter of perspective.
congrats, you're on step 1 of waking up from illuminati propaganda - i mean... what?
in all seriousness though, good and evil are both perspective and "black and white."
on the perspective side is order and chaos. think of order like a dictatorship - theres an absolute authority that controls everything, usually giving no freedoms to the people, but keeps them safe with laws and a domestic force for protection - keeps everything in order (duh). the people don't have many social freedoms but live comfortable.
chaos is like a world without laws. you can live peacefully if you choose with your freedoms, but that doesn't mean everyone else will, and they will probably hurt you to benefit themselves. that's true chaos anyways, though even hell is able to have some order to keep armies together and the prime evils at the top.
conclusion: too much order = bad, too much chaos = bad. middle ground? probably good, but it depends on how much order you think is good/bad and how much chaos you consider good/bad
now on to the black and white! good is obviously peace, loving, joy, happiness - any word associated with positive emotions and actions. why? because it makes you feel good and is good for others! if you are a person who lives closer along these lines, you're probably going to be a good guy
and evil is anyone who inflicts pain, suffering, yadda yadda.... so on so forth. but TRUE evil would disguise itself as a benevolent being and mislead everyone until a sudden moment where they are in full control - order?
christianity - you have jesus. a good guy who is peaceful, loving, compassionate. then you have the guys that made his church which basically said "look, jesus was a good guy - if you don't like him then you dont like good, ergo you are evil. oh and by the way we are the only ones who can speak to him so you must do as we say"
and THAT'S how you get your paladins who kill without question!
game worlds use archetypes like your cliche paladin and his nemesis because they are the most simple to explain. otherwise you get a crazy complex world like the explanation i just gave you.