It's cruel. Don't do it. Train your cat not to scratch your furniture. It's not that hard. It is nontrivial. Some cats do not believe in training.
I'm all for getting animals fixed, but to say that the pet is not adversely affected is just strange. It usually changes their metabolism and their behavior.
We got one of our cats declawed and will not do it again (though since my son is slightly allergic it made that decision easier since all of our future cats will be outside). Stretch was declawed at about 9 months and, per usual, the vet did not really go into what was involved. It requires removing everything the claw grows from and as such is analagous to removing your finger at the last knuckle. He seemed to respond OK, but we worried about him a lot when he got out (and he was an escape artist).
I've heard people say that cats like companions but every cat my family has had and women I've dated don't seem to like other cats. A lot of them like people and will get jealous when other cats are around and their people get more attention.
Might as well cut off the cats whiskers too. I'm kidding obviously but as you can see I am against declawing.
Just a couple of notes... Getting cats spayed or neutered is actually healthier for them than leaving them un-fixed. Domesticated animals (dogs and cats) live longer, healthier lives when they are fixed because it eliminates a number of potential health risks associated both with the organs as well as with things like going through "heat." It is also a responsible thing to do for the world animal population if you don't intend on breeding an animal. The lack of animal sterilization in America alone leads to hundreds of thousands of animals being destroyed each year and others suffering and/or spreading disease. As to the question of why people keep multiple cats more than dogs. Cats are just easier. You don't have to walk them. They aren't as high maintenance as dogs in general. Also, cats have very organized social structures when kept in groups. Once they find an equilibrium within that group, they often thrive.
As a first time car owner, how can you tell if your cat is an out door/in door cat? Do you just let the cat go outside and monitor them to see if they would stick around and not run away? We always kept Morris inside for fear that he might run away for good and he doesn't mind staying inside.
Also, cats don't smell up the house like dogs do. If the cat is pissing on the carpet, it's probably because the litterbox isn't being cleaned like it should. Just clean that litterbox every day and the cat will take care of everything else. They're very clean by nature. That's why they're always licking themselves.
My cat was declawed when she was a kitten. The only thing that she doesn't seem to understand is covering up her poop. So we bought one of those automatic litter box thingies. It kicks as and there is never a scent and we just have to occasionally add litter to it and toss the waste containers. Well worth the mulah.
Personally, I wouldn't let them out unless they were already outside previously, particularly in urban areas where they could fight with other cats and contract serious diseases (like FIV) or in suburban areas where they could be attacked by a predator like a raccoon or oppossum.
As a first time car owner, how can you tell if your cat is an out door/in door cat? If you open the door and the cat takes no prisoners on the way out, your cat might be an outdoor cat. Seriously, your car will let you his/her preferences, removing the guess work on your part.