I had several cats in the past and have one cat here. They all have never been declawed. They all have never scratched any furnitures here. When I first bought each kitten/cat home, I watched them careful and if they started to scratch on furniture, I went and squeezed their paws and at the same time I said in firm "NO NO" even sign languages too. Usually after second time they have learned and never had any problem since then. Every week or two I alway trimmed their sharp nails to keep in short.
Let me tell you a story or two ...
One time at the Vets one of my cats, Gandalf was mad at the vets and went boxing at me especially at my face as I hold him. The vets went back few steps and was in shocked. The vets checked on me to see if any scratches on my face and hands, NOPE .. NONE... cuz Gandalf didn't use his claws cuz he knews he is not suppose to use his nails no matter what. Very smart, wasn't he. haha
Also Gandalf was attacked by two pit bull dogs out in my front porch. I was doing landscaping and saw them. I ran to them and kicked both dogs to get out of way then Gandalf ran up to the tree. Thanks God he used his claws. Finally both dogs ran to their owner's vehicle about a half block away as my neighbors saw. Boy he went through alot and had two surgeries and survived very well. Whew. The vets said Gandalf was an amazing tough cat!!! haha
Also one of my cats, Bandit was playing with a garden snake that I found them playing in my living room behind crouch!!! It was funny cuz the snake is afraid of Bandit, perhaps he used his claws when it's really neccessary!!! haha ... well we finally got that snake out of house tho.
Well I personally believe all cats shouldn't be declawed. It's NOT hard to train any cats NOT to use their claws. It's simple only been told twice then they won't do it again in the house (except scratching pole when they have been told "OK, good boy/girl).