BOTH WAYS
If a modicum of evil can infect an entire body of good, then it would follow that a modicum of good can also disinfect an entire body of evil.
No body and nobody is entirely evil nor entirely good. Such is given to be humanity's plight on this planet: To be cosmic spirits encased in man's human flesh. Knowing little, and sensing less, yet still here, still alive; still grateful for God's grace.
Amen.