If a cat is taught from the beginning not to scratch furniture and their claws are kept trimmed then there should not ever be an issue about them scratching. If they are not easily teachable there are tons of websites available to teach you how to teach them. But I guess instead of taking the time to teach your cat not to scratch it's much easier to take away their claws.
Just as a warning - declawing will not stop them from still using the furniture arms to "scratch". Just because you took away the claws does not mean you took away the ingrained instinct to scratch. After time this action will wear on your furniture as well and cause damage.
Canada and the US are the only two countries holding out on not banning this horrendous practice. What does that tell you except that we are waaaayyy behind the times. Both in vet practices and animal cruelty.