The cyclops is a monster because he sees with only one eye - with only one viewpoint, one perspective.
Without the context provided by additional perspectives, all his information is tortured out of shape by his mind to fit the only perspective he has. The mind of a cyclops is a Procrustean bed, named after the mythological Greek criminal Procrustes who tortured and killed travelers by altering them until they exactly fit his bed for guests. Every observation, every "fact," every idea is stretched, truncated, folded, spindled, or otherwise mutilated to make it fit into the one viewpoint the cyclops has. By the time the cyclops is done "thinking" about an idea, it bears only the faintest resemblance to reality - though from his one perspective it's a perfect fit.
A single perspective cannot have perspective on itself, so the cyclops is incapable of introspection. Introspection is the capacity to consider oneself - especially one's ways of thinking about the world. It is a prerequisite for significant personal mental development, since until a person achieves introspection he is inclined to believe everything he believes, to take for granted everything he takes for granted. That is, he is blind to himself. His inner eye is closed, so that he walks through life asleep, dreaming a fantasy that bears only a passing resemblance to reality.
Nor does a cyclops have true empathy. The cyclops's eye creates a self-centered perspective, in which the world is perceived only in relation to oneself. As the Native American saying goes, you cannot understand another man until you walk a mile in his moccasins, until you see the world the way he sees it. That requires an act of imagination, opening the mental eye to new possibilities outside one's own perspective, something a cyclops cannot do. This is why the cyclops is so often a cannibal. Without empathy, other people seem to be just phenomena like cattle or rain, of no special importance except as servants or raw materials. A human being without empathy is a sociopath.
Every human being is born a cyclops. Our two biological eyes create a binocular outward vision, but do nothing to improve our perspective on ourselves or our ideas about the world. We still have only one mental eye, and we assume it is correct - without imagination it is impossible to assume otherwise. That is, we appear to be binocular creatures, but in all the ways that matter we are all cyclopses.
As far as we can tell, in the same way a human being has an instinctual drive for language that must be cultivated to blossom into full expression, so do human beings have an instinctual drive to open up their third eye, to acquire a binocular mind and become capable of introspection, empathy, and the other traits that make human beings more than just monsters. Curiosity is built into the healthy child and will readily develop into imagination given the chance. Parenting and culture are needed to help the child with that passage through the culture crisis; they act as midwives for this second birth. When they go wrong, this path of development withers and an infant's naive cyclopean state ossifies into the hostile cyclopean mind we see all too often in "adults."
Heraclitus wrote "Eyes and ears are bad witnesses for people who have barbarian souls." He was thinking of the cyclops in all of us that we must overcome if we are ever to have a meaningful relationship with the real world.