I love the "bad apple" metaphor because when you remember to say the whole thing it becomes clear that it is actually an argument against ignoring issues in an organization because only a few people are the "cause". If a police department "only has a few bad apples" then (according to the metaphor) those bad apples must be removed swiftly and decisively or the integrity of the entire department will be compromised.
I love this "bad apple" tidbit, it's going in the top drawer of the toolbox. :D
Relevant SMBC http://www.smbc-comics.com/index.php?db=comics&id=3025#comic
Prove that. You can't, cause it's a negative. It seems much, much more likely that "The times these things are uncovered and get national press attention is rare." For the few times that are, how many are not, 10x? 100x? I can't know, but I 100% doubt we catch 100% of these things.