If declawed cats are less able to indulge in their murderous ways, it can be the case that something somewhat cruel to cats is nevertheless on net animal welfare increasing. And, it seems a fairly appropriate way of internalising the relevant externality: the cat gets to exist,
Imagine yourself behind the Veil. You do not know whether you will be born a cat or a bird. In the state of the world in which cats are declawed, you are more likely to get to exist, get to exist as a cat, have a less happy life if a cat, and have a happier life if a bird. Do you, behind the veil, choose to prohibit, allow, or mandate declawing? It'll depend on how unhappy declawing makes cats, and how much effect declawing has on cats' ability to torment birds. The first isn't easy to assess, though I'd definitely pick declawed cat over non-existence. Does anybody know anything about the second?
Declawing: to help reduce the risk.
Conflict of interest watch: after our eventual extensive home repairs (earthquake), we'll likely have to get another cat. I prefer that that cat be declawed even counting the losses to the cat. I don't think this colours my analysis above.