One Bad Apple spoils the whole bunch is the saying.
Forget the Micheal Jackson song. I'm tired of organizations saying "well, it's just one bad Apple".
No, the saying indicates if you find one bad apple, you have to inspect the lot and quickly get rid of all the bad apples. Not excuse the obvious one and say all the rest are good.
The saying goes back to the Middle Ages, and basically compares the endeavour of either putting apples up for winter and/or making Apple Cider with any group effort - a wormy or rotting apple only takes a day or so to affect all the apples around it, and that infection expands like a zombie apocalypse.
If you have one bad actor in a group of people, s/he quickly taints the rest of the group and what they trying to accomplish along with any respect that group may be trying to gain.
it's often used by right-wingers in the context of defending the police, arguing that the police as a whole are great and we should support and respect them, even if there are "a few bad apples" (though they seem to be quite fervent in supporting the bad apples as well...).
yet these same people will denounce entire groups on the basis of the actions of a few. for instance, the gleefully slam a billion muslims base on the actions of a few violent extremists. you'll never hear them say it was just a few bad apples when it's a minority or other group lower in their idea of a social hierarchy.
It isn't usually the individuals themselves that are the problem, but the culture.
Weeding out the bad apples only takes care of the bad apples dumb enough to get caught.
It was always harder to carefully weed through the bad apples in time to save a few apples before they went into the press than to just get a new crate and quickly sort.
Since he practiced making cider the way his grandparents who learned from their grandparents did, I suspect that was usual practice back in the day.
Toss the crate and start over.
The "good" apples ignore the bad behavior of the few "bad" ones, and then they are all bad ones.