I dont know if this has ever been addressed in the history of theology, but this has been something that has constantly bothered me. On one hand, the optimistic outlook does not recognize the existence of evil, while the pessimistic outlook does not recognize reality as ultimately good. It seems like the only options for pessimism is moral dualism and with optimism can lead to moral relativism. Frankly to deny the existence of evil, one would have to be extremely ignorant and pampered or be a cold person. Yet being “against” puts one at risk of harboring hatred, pride and malevolence. I have sometimes seen people resort to bland compromises(as Chesterton calls them) in affirming a little optimism and a little pessimism. Such as reducing all morality to one single issue, adhering to “might makes right” ideologies, going with the just world theory, entertaining “paradise lost” propaganda(such as the noble savage myth) or postmodern nihilism.
I know that we have used philosophical abstract models to understand the nature of evil. Such as the stance that evil is the absence of good, and therefore saying no to a no is a yes. On paper, this is an excellent answer to explain the problem of evil, and on paper works. But in practice is a much more difficult concept to live under. But this maybe just the limitations on human language, due to the nature of words being inherently dualistic. I will admit that poetry is a whole different.