That's a good point I forgot to account for. But it can be accounted for: even if we stipulate that it's not ethical to acquire genetically compromised dogs purely for aesthetic reasons, there are other attributes of these dogs breeds that make them more suitable than others. For us, it was a requirement that the dog be content on its own, amiable with other dogs and children, and not excessively demanding of exercise that we'd be unable to provide it (we're simply not around most of the day).

Were no dog available that could reliably provide those attributes, our choice would certainly have been not to acquire a second dog.

But I also think, for what it's worth, that it's still ethically tricky to dispose of the question of whether it's unethical to select dogs for appearance. I think you can predict the argument I'd make there.