Some folks equate using evil with doing evil. I’d add that folks like this tend to be impervious to reason, so I’m not writing this for their benefit.
However, there’s a rather obvious distinction between doing evil and using evil. A few examples should suffice.
A 22-year-old is murdered. He was in perfect health. Cut down in the prime of life. His vital organs were in pristine condition at the time of death.
Suppose his organs can be transplanted to save the lives of half a dozen terminal patients?
Murdering the 22-year-old was evil. But is it evil to use his organs as a means of saving the lives of half a dozen terminal patients? Is the surgeon morally equivalent to the murderer?
The surgeon is making use of evil-the evil of his unjust demise–to do good. Does that make the murder good in itself?
Take another example: totalitarian regimes typically divert their finest scientific minds into weapons programs to further the imperial ambitions of the regime. And it’s evil to help the regime do evil. It’s evil to empower an evil regime. Evil to enhance its ability to perpetrate even greater evil.
But scientists sometimes defect. Indeed, our intelligence agencies try to turn them. Encourage them to defect. We give them asylum so that we can debrief them and find out what our enemies are up to. Learn about the R&D programs.
What the scientist did was evil. It was evil for him to use his scientific genius to improve the weaponry of an evil regime.
But is it evil for us to give him asylum so that we can debrief him? Is it evil for us to exploit that situation so that we can know whatever the enemy knows? So that we can take countermeasures? Is that inherently evil?
Take another example: suppose the enemy is plotting an unprovoked attack on one of our cities. Suppose we intercept encrypted messages which alert us to the attack. Suppose we can use our advance knowledge of the plot to foil the plot. Our enemy was planning to do us evil. Is it evil for us to use that information to defend ourselves? Or would that be tainted fruit? Fruit from a poisonous tree? You decide.