Nothing will ever convince declawing is acceptable in any but the most extreme circumstances. Saying 'it was the only way we were allowed to have a cat' is about equal to saying 'we had to keep the stallion intact or daddy/whoever wouldn't let us keep him'. EDUCATE people. There is no justification.
There's a reason its illegal or considered extremely inhuman in almost all developed countries (looked at a list and it is in way more than I thought).

It is totally incomparable to spay/neuter. It's the quality of the ANIMAL'S life we're talking about, and remaining intact, you cannot say, wouldn't have a negative impact maybe not necessarily for one particular animal but for every single one it created or for every one its offspring pushed out of a home.
For whoever said their cat is spayed only for convenience and wouldn't go outside so wouldn't get pregnant - I'm pretty sure if she wasn't it'd be pretty damn hard to keep her away from any males that came a-courting.
To compare the two is just ridiculous.

The UK doesn't 'do' indoor cats, as I've said, but I do see the reason it's different in the US: we have no rabies, no dangerous predators (there are stories of foxes attacking cats but pretty unsubstantiated - one of ours used to sit and play with their cubs in the driveway), people don't have guns to shoot them and its pretty damn unlikely they'll meet our one poisonous snake. There are cars, of course, and personally I'd never have a cat if I lived next to a busy road (in a culdesac right now) but the risk's still pretty low. I was actually pretty SHOCKED the first time I learnt lots of Americans didn't let their cats outdoors whenever they wanted and it took me a while to understand why!
It's a risk management thing. Keeping an 'indoor' cat here is simply not worth the negative adjustment to their lives in order to counteract that risk. Where the risk is higher, like in the US, good on you for keeping your cats safe, although it does mean you have to make changes yourself in order to keep the cats happy. I do believe that, unless it's cat that have never been outside in its whole life, there is no cat who doesn't want to - it's only fear of the unknown because they've been kept away from it by humans - I've never met a cat that, in good weather, didn't choose to spend at least 50% of its time outdoors.
I also do think a lot of people in the US demonize the practice of allowing cats outdoors far too much, hence the real/percieved comment. I've had teenage girls yell at me 'OMG if you let your cat outdoors it will DIE! Outdoor cats only live an average of ONE YEAR!!!' even after they knew I was British. Er...yeah. I've had 4 cats now and the ones that have passed have lived to 18 (liver failure), 16 (mysterious hindquarters paralysis) and 14 (feline HIV got to him in the end - yes an outdoor cat lived to his mid-teens likely having HIV his whole life! we put him down as soon as we knew about it).
I've never met an indoor cat. I know some show people keep their very expensive ones indoors here though. I think it's the same as people who show keeping their horses stabled 24/7. Bit sad for the animal - it didn't choose to be expensive.