Can you help me understand how an extant dog could have a desire to live so ethically powerful that it overrides suffering, while it being simultaneously the case that it is unethical to bring such a dog into existence? It seems to me that your (a) implies that a living dog suffering from these defects is generating some benefit from living. Isn't it: maximum benefit > some benefit > no benefit?

That's a good question. I suppose I'm arguing for ethical framework in which I'm not the sole judge of costs and benefits.

I think the pug will suffer so much that its life is not worth living. But if the pug feels differently then to some degree I should respect that.

I guess my view is shaped by my empathy for the dog. How would I feel in his situation? Similarly, if I end up in a hospital bed racked with pain, do I want the doctor to make a cost-benefit analysis without regard for my own feelings?

Respectfully I want to creep up towards a presumptuous argument and say that you won't argue for euthanizing pugs because your gut tells you that whatever trouble pugs have due to their (many) health problems, a well-cared-for pug is generally a happy dog, and is not in fact living a life of overwhelming suffering.

We own a rescue mutt and a brachy purebred, and while I can't get inside the heads of either of my dogs, I would have absolutely no trouble telling you which of the two dogs is enjoying its life more. :)