The phrase "a small evil" is correct and usable in written English.
It can be used to describe a minor wrongdoing or a lesser form of harm that is considered acceptable or necessary in a particular context.
Example: "While lying is generally wrong, sometimes telling a small evil can spare someone's feelings."
Alternatives: "a minor wrongdoing" or "a little vice".
"Compared to other forms of political persecution, the denial of the right to return home seems like a small evil," said Hu Ping, the editor of a pro-democracy journal in New York who has not been allowed to see family members in China since 1987.
He comes along for the ride, determined to have as much fun as one possibly can with Islamic radicals, white supremacists, Christian separatists and assorted conspiracy theorists, all of whom are convinced in some fashion that a small, evil cabal is secretly planning to take over the world.
These are the pleasures of her small, evil little life.
The best service a chaplain provides for a patient who is not religious (that is, most patients) is treating them not as a symptom or a saint but as a whole person, complete with the pack of small evils all of us contain alongside our better angels.
It was she who changed the name of Obelix's small, evil-tempered dog from Idéfix to Dogmatix, and transformed Panoramix into Getafix, provoking decades of scholarly musing as to whether the druid was a dopehead.
It's small evils so you can share the joy of the theater on social media.
But in the words of Screwtape, "Small evils are what corrupt humans, not large ones".
Created by a small team at Evil Twin Artworks, it's an intriguing mix of exploration and battle management.
But in a neat example of a small act of evil being committed to stop a greater one, Rick rigs the roulette table so that her husband wins enough money to buy their way out, and her dignity is spared.
A small group of evil 14-year-old boys get together in the guts of an abandoned factory and build a robot to do their evil bidding.
