Everyone has to decide for themselves precisely where they will draw the line between save & cull, and few deserve criticism for where their personal line is drawn. Some will go to extreme measures & expense to preserve or extend an animal's life, others will not or can not.
Personally, the place where my line is drawn is determined by economy and quality of life. I can/will not spend much on professional treatment for any animal (that's one reason I'm so grateful for this forum for instructing me in poultry care!) but if the animal doesn't seem to be miserable, I'll give it a chance to live.
I once had a chick who developed a crossed beak when it was a few weeks old. I also surveyed my online poultry pals, and also got a variety of opinions. But this chick didn't seem to be suffering, in fact he had an admirable amount of pluck! So I didn't cull him, and he lived a seemingly happy (though short) life, and provided us with much pleasure & delight.
I don't know how to create the link, but you can do a search for my post titled "Eulogy for a great little rooster" to read more about this bird.