Existence is the state of being perceived, by the perceiver. Real things are strong, distinct, vivid ideas whereas imaginary things are weak, indistinct and faint ideas.
A Treatise Concerning The Principle Of Human Knowledge, George Berkeley
The ability to feel and perceive things around us is unique. If things are real, then there must be things that are unreal, imaginary. If real things are dictated by our understanding and perception of our senses, then how will we ever know when they fail to distinguish between the realities and fantasies.
Bad things are necessary for the existence of the good things. And all the horrible realities will be the prerequisites of parallel realities in the realm of goodness. Because, without the existence of darkness, how will we know that there is brightness. Without white, how then would it be possible for black to exist?
Mere existence of human, necessitates the existence of inhuman. Of those who choose not to think, of those who simply put desires and emotions above wisdom (logos).