Some people think declawing is cruel and some people don't. The thing is this: the declawing of cats only happens in one region, North America - the USA and Canada. Many countries would consider it animal cruelty under their animal cruelty laws. I am referring to European countries.
In the UK if a veterinarian declawed a cat for the convenience of the cat's owner the vet could be prosecuted under the Animal Welfare Act 2006 for animal cruelty (section 4 Unnecessary suffering would be applicable amongst other sections I suspect). It just does not happen in the UK. No one considers it as an option. It is not in the mind. Most people have not heard of it, probably.
On that basis alone we have to conclude that declawing cats is cruel. How do you define cruelty? The dictionary definition is: "causing pain or suffering".
On that simple definition cat declawing is cruel because it is a very painful operation despite painkillers which are given these days. In the past pain killers were not given sometimes as I recall reading somewhere. The idea was to make sure the cat did not put pressure on her paws to prevent re-opening the wound. Now that really is very cruel.
It is not just the physical pain associated with amputating the last joint of the ten toes of the forepaws (sometimes all for paws are declawed though). There is good evidence that some cats suffer psychological pain too. Unfortunately it is hard to obtain solid scientific information on this sort of subject.