Well, dear, spaying/neutering has quite a lot of health benefits for the animal, as well as controlling the population of unwanted/abused/neglected companion animals. After vaccinating, spaying/neutering is the single most important step a pet owner can take to safeguard their pet’s health. If you want to put your couch in the same category as your health, roll your eyes till they fall out. Otherwise, you might do a bit more research before making asinine comments.
As for the OP, if you have such a moral duty to make sure that nothing gets scratched or otherwise damaged, maybe you shouldn’t have a cat at all. Declawed cats still go through the motions of scratching, swatting, etc., and I’ve known a few to get so frustrated with the ineffectiveness of swatting that they turned to bunny kicking and biting. This is personality-dependent, of course, just as the effectiveness of non-declawing alternatives is. (FTR, training and trimming works very well indeed for a lot of cats.)
And no, it has nothing to do with the rarity of the breed. Quite a lot of animal rescue groups and shelters have no-declawing clauses in their adoption contracts, even though they rarely get anything but domestic short hairs.
You say you’ve got kids to think about, and I think that’s the single most compelling reason you have to either live with the claws or not get the cat. You’re talking about deliberately, with pre-meditation, breaking a promise, as long as it gets you what you want. Is that the message you want to send to your kids? That it’s all right to lie to get what you want, as long as you don’t get caught? That you should only keep promises that are convenient for you?
You say you have a moral responsibility to your kids to have this cat declawed–I’d say you have a moral responsibility to them to be an honest, upright, decent human being so they may learn by example.