Quote: Absolutely not. That is, in fact, almost verbatim for my stance on it. The future cases validate the current case in most instances. The "cull and replace" method of dealing with illness or injury doesn't actually cut your losses as much as it may seem, because there is still the cost of raising replacements to consider. Also, immunity is often an undervalued necessity in this day and age of closing borders and culling entire populations to control disease. People are culling for the equivalent of the common cold, so they just replace with more weak stock and hope they don't catch it again; it's wiser in many cases to support the development of natural immunity instead of cull, and breed on with the stronger stock.
It's difficult as you learn but once you gain experience, you will be able to save animals that are being put down for the equivalent of a stubbed toe... You'll also be able to save cases so bad people will basically demand you put the animals out of their misery. (The misery in question is usually the human's. As long as an animal is willing to fight for its life there is a very good chance. I've saved many animals that looked like lost causes; quite often it's not as bad as it looks, and the cases that don't look so bad are often the real bad ones).
It's one thing to cull an animal that's ill or injured because you don't think you'll ever want to breed that specific individual. After all it will never "pay its way" if you treat it, as they say. It seems logical. But my reasoning on going the extra mile and learning how to fix rather than cull is that what happens when the injured or ill animal is the irreplaceable culmination of your years of careful breeding? Cull, because that's all you ever bothered to learn? Or what if it's a pet? Much of what you learn for any species' health applies to some extent to other species.
I could have lost some of my best animals so many times over if I'd given up. If you don't try, you'll never know. Sometimes there will be failures to save an animal, and it sure doesn't feel encouraging when that happens, but if you educate yourself and persist, you'll save far more animals than you'll lose. I've obtained some of the greatest animals I've ever known because they'd ended up special needs somehow or another, through no fault of their own... I got them as rejects and they have more than paid their way, over and over again. Totally worth it in every way, for me.
Best wishes.