The quick answer to this question is that declawing is the equivalent to cutting your finger off at your top knuckle- it is an amputation. A cat's nails are a natural defense mechanism. When you take its nails away, you may alter its personality. A lot of cats that are declawed are known to bite more, demonstrate aggressive behavior. Scratching is an instinct in cats, you cannot stop it - you MUST try to direct this natural instinct by having scratchers, cat trees - items that are acceptable for the cat to scratch on.
It is actually illegal in most parts of Europe to declaw cats because it is considered inhuman. Here are just the beginning of many good articles on declawing.
Alternatives to declawing:
This is very important - especially for Sphynx. Sphynx should not be allowed to outside for long periods of time - they can get sunburned and so not tolerate the cold very well. They also should never be allowed outside unsupervised.
Nearly all cats should be kept inside. A cat who is keep indoors generally leads a happier, healthier life.
Also, Sphynx taken out in the sun tend to get unattractive pigment spots.
The link below has a story that much better describes why not to let your cat out... after you read this... I doubt you will ever think about letting your cat out again.
Our animal population is wildly out of control - you can just look at all the shelters filled with cats and dogs. It is important to ensure that your animal is altered so he or she does not reproduce unwanted kittens adding to the population of homeless animals.
Again some more articles that say it well:
MYTHS ABOUT SPAYING AND NEUTERING
The science behind spaying and neutering