We all have our own definition on what should be euthanize and what should not, it's a hard call.
For me any animal that fails to thrive, whether it's eating on it's own or limited in his movement because of neurological issue or physical issue is euthanized. In other word if the quality of life is not there the animal should not suffer because of his owner or breeder not being able to make the right call.
Minor kink, under bite, missing eye around here mean pets, who usually remains in my care until the right person comes along (someone who does not intend to breed) and want to offer a good life to a special animal.
Now I can tell you that some people will cull any animal that is not perfect which is not unique to the snake industry.