More generally, aphorisms and allegory are specifically created to prove a point. They can never constitute evidence, only persuasion.

The early bird gets the worm, but the second mouse gets the cheese, and all that.

Perhaps a good expression is "A few bad Apple employees^W^Wapples spoil the barrel".

In other words, the decay started by a few will quickly rot an entire batch, if the good and the bad are kept together too long.