I have such a mouth when it comes to declawing and I never shut up about it. there is a thread that was started here about declawing and web sites to gain further info. Show it to your friend. Sandy posted a link here in this thread.
I also had a friend and he had a cat for 18 years and it died in his bathroom one day. He had that cat declawed and decided if he was going to get another cat he would declaw front and back. I was such a nagger about it, I argued constantly, he too said there was no emotional damage done to the cat. Until one day when we sat down and we started to talk about this scared unfriendly animal, who would not listen to authority, the kitty would hiss at him anytime he would raise his voice. The more I kept on him about it the more he understood, I sent him websites on the issues and told him to do research and if he still agreed with declawing I would stand aside. Well it worked he has two beautiful Bengals who are completely spoiled claws and all!
Good luck to you I truly hope you get through to your friend.