Incredibly painful? To use a litterbox? Seriously? Where did you get this? I don't know any cats who will willingly do something that's "incredibly painful," and yet millions of declawed cats have used litterboxes for decades without issue.
Yes, incredibly painful. Between phantom limb pain and the early onset of arthritis due to the toe amputation, it becomes increasingly painful for cats to use the litterbox.
90% of cats with litterbox aversion have been declawed (the other 10% are comprised of cats that have recurrent UTIs, crystals, and anxiety).
These statistics have been reported by the ASPCA, the American Veterinary Medicine Association, and the HSUS.
I don't understand why people sit here and say "But it doesn't apply to me because________". The procedure has been outlawed in many countries, and several cities in the US. Research supports the fact that it is a painful procedure that impairs the life of the cat.
It's something that is insanely selfish to do when there are humane alternatives such as soft paws. It's not that hard to train a cat to scratch appropriately and trim their nails weekly or bi-weekly.
In a study published in the January, 2001 JAVMA, 33% of 39 (1 in 3) cats that underwent onychectomy developed "at least" one behavior problem immediately after surgery, with the most common problems being litter box problems and biting.
In a retrospective phone survey, Patronek found that among 218 cats relinquished to a shelter,
52.4% of declawed cats versus 29.1% of non-clawed cats were reported to have inappropriate elimination..."
Borchelt and Voith, looking only at aggressive behavior in a retrospective survey of pet owners, found declawed cats bit family members more often than did non-declawed cats.
(Sorry I don't have the articles cited, my works cited page is on my home computer, and I'm traveling right now).
Those risks are not risks I'm willing to take with my own cats, and yes, I do judge people who maim their pets for life just because it makes the owner's life easier.