I don't know how much this is true today, but in years past, a horse with a broken leg was immediately euthanised in the manner of the day, because it was next to impossible to set and get the bone to heal, and it was almost certainly a long agonizing period before the horse died of complications.
The line is actually an excerpt from a joke, which wasn't particularly important to the analogy tho funny. A man is pulling a trailer full of horses, wrecks, goes down an embankment. The man survives but has a broken arm. The sheriff pulls up on the accident, the man is up walking around checking on the horses. They come up to the first horse and the sheriff asks "What's wrong with this horse". "He has a broken leg" and the sheriff immediately pulls out his gun and shoots it. Next horse, "Broke neck" <Blam>. What about him, "Broke leg" <Blam>. Then the sheriff asks the man "What about you - are you hurt?" The man immediately blurts out "Nope, I'm just fine, thank you for asking."
Now back to fungus eaten lenses - I realize that there may be permanent etching of the lens, but it just strikes me as giving up too quickly (to save the other lenses in the building) to not attempt to clean or (or replace - we ARE talking about the factory after all) elements with fungus.
