Romans 5:12: Wherefore, as by one one sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:
1 Corinthians 15:21a: For since by man came death....
1 Corinthians 15:22a: For as in Adam all die....
And we can think of this on the lower, more ordinary scale.
One sinner can do damage to his fellow man. That migtht be the drunk driver who takes innocent life. The thief who steals. The murderer who kills. The liar who bears false witness.
In a family one sinner can destroy much good. A husband or wife can abandon covenant responsibilities in the name of personal "happiness" and innocent lives can be scarred and broken.
In a church one sinner can destroy much good. Sadly, I have seen one malcontent sometime be able to stir up dissent and disagreement where none existed. Consider: