Getting a cat declawed, besides for medical reasons, is a unnecessary and inhumane process.
Declawing a human would be equivalent to cutting off the first bone in the knuckle. It is painful and irritating for the cat; leading to swelling, loss of balance, and general discomfort. You are literally amputating a portion of the cat's paw. Not only do declawed cats have difficulty defending themselves, but they also are not able to exercise their natural scratching behavior. If you can't have the whole cat, don't get one!
A comparison of declawing a cat to declawing a human:
https://consciouscompanion2012.files.wordpress.com/2015/03/finger_2.jpg