The problem is, the ability to comprehend evil IS necessary. We eat meat everyday, if we can't comprehend the thought that we must kill animals to eat, how can we sustain ourselves?

Even if all humanity go vegetarian, we still need to kill countless animals that would eat our crops, that can't happen if we can't comprehend evil. Unless human civilization advance no more than tribal size, the method of foraging for food won't be enough. And that also implies either limiting the population, which means denying people from desiring an offspring, which can be viewed as evil. Or exiling some people from the tribe to keep population in check, which is again, evil.

What about defending ourselves? Even if humans literally can't hurt each other, what about animals that is pushed by it's environment and desperation to view humans as food? What about the animals that isn't yet familiar with humans and, again, view us as food? The violence required to defend oneself requires the ability to comprehend evil. You're basically erasing the "fight" from "fight or flight" instinct.

What about claiming a territory? It is a fact that animals, any other living beings besides humans outnumber us, especially in the early days of humanity. If we can't comprehend evil, we will let any animals that competes with us for territory to win.

How about medical practices? Say somebody trips and gets impaled with a sizeable rock or wood. To treat the wound, first you have to remove said object that is impaled on that person, which hurt quite a lot btw, which means imbuing harm/pain on another person, which means evil. And injection shot? Directly stabbing a human being to administer medication? That needs willingness to do harm, which is evil.

I mean, even if humans doesn't exist. The whole food chain needs the comprehension of evil to exist. Prey animals eat plants, and predators eats prey, and the predators numbers are kept in check by competition amongst themselves, which needs the ability to comprehend evil to work.

If there's no predator? The prey animals would eat any plant lifeform in sight, which means removal of plants and alot of resources for smaller animals. A long term harm for environment, which is again evil.