I have been speaking to an American friend, who indeed had her first cat declawed, and it appears that our attitudes to animals are driven by our culture. She considered the practice as normal and perfectly acceptable, although I and some other English friends have managed to change her mind slightly. In America, apart from the declawing (and debarking) issue, there is the fact that unhomed cats are regularly put down in animal shelters.
This seems appalling, but when it's a cultural issue it's very difficult to deal with, and each country has its own area of barbarism built into its culture. As an example, until recently we were happy to hunt foxes with dogs. And indeed, I am old enough to remember when the practice of foxhunting was actually *endorsed* by the RSPCA!
Yes, we should work to educate where possible, and it is quite right to express our abhorrence about the practice on forums. But I think we should guard against feeling too superior about the issue, because we are all living in glasshouses.