There is no such thing as “good,” without having “bad.” Part of how each of us defines something is relative to its counterparts.
How can you know (in a personal sense, or even as an idea/concept of) one thing without knowing the spectrum in which it falls into.
Maybe the world could be wonderful without pain, despair, violence, death, etc.. But by losing those, you lose love, bliss, happiness, peace, kindness, etc…
We can still strive to make a better world, but never a world of endless gray where everything is just “fine.”