Bad apples and barrels are a bad metaphor because there's been efforts made to claim that good apples stay good when beside bad apples. To avoid this confusion

Bad apples and barrels are a bad metaphor because there's been efforts made to claim that good apples stay good when beside bad apples. To avoid this confusion, you can refer to rolling a ball on a curve. A ball at the top of a hill is the bad apple case - any nudge and the ball will roll down. A ball in a valley will always roll down till it's at the bottom.