@NeverDropYourMooncup
We aren't ever going to run out of kittens. There will still be strays as a direct result of them following the hormonal urges to escape from not being spayed/neutered. You only need one unneutered Tom and unspayed female cat escaping to cause a population explosion in a year -
On escape - 2 cats
1st mating - 2 cats + 4-12 kittens = 4 to 14 animals
2nd mating a few weeks later - 4 to 14 from 1st + 4 to 12 kittens = 8 to 26 animals
The first litter reach sexual maturity around 4 - 6 months, assume half are female and they've been mated by their father = 26 animals plus (13 females times 4 to 12 kittens each) = over a hundred animals.
and then there's the 2nd litter reaching maturity = hundreds of animals in less than a year.
We are never going to run out of cats.
That's an interesting little set of figures, and you are probably on the money if a few cats escape and don't get neutered... But what I actually said is what if every single cat is neutered, EVERY SINGLE CAT. I am not interested in the ones who escape before they are neutered...
And the posts calling my question 'silly' and LOL-ing at it, saying 'ha ha ha as if we will run out of cats' clearly couldn't be arsed to read my post properly. Saying 'oooh there's 1000s of cats in Saudi/Greece/China blah blah blah...' is moot, because there won't be any in any country, if every bloody cat is neutered when they are very young WILL there? 
So the question still stands although we are all encouraged to neuter our cats (and I was quite happy to do mine...) What if EVERY cat was neutered? No, actually don't bother answering, because I can tell you what will happen...... The species will end. That is a fact. (Or maybe that's what some people want.)
Maybe we should instantly neuter every single puppy too, even the pedigree ones. Why not? It's OK to do it to all the cats! So why not do all the dogs too? Let that species die out too. I'm sure a bunch of dog lovers will come along soon, and say 'but dogs don't wander freely like cats do' and that is partly true. I say 'partly' because I see LOADS of dog owners, with their dog off its lead, wandering about, sniffing around other dogs, jumping up people, knocking over children, pissing up lamp-posts, shitting on the footpath, and wandering off away from its owner and yep 'shagging' other dogs...
There is also the fact that 1000s and 1000s of dogs are abandoned every year, and end up stuck in a dogs home, and eventually euthanised because nobody wants them. So the same strict neutering 'rule' should also apply to dogs!
As I said, I was happy to neuter my cats, and am not totally against it, but people don't seem happy to admit that if every cat was neutered, the species would end. And it would! Are people not acknowledging this because it suits them not to admit it's true?
I also disagree with the poster saying pet ownership should end one day, along with circuses and zoos. A cat or dog in a family home will no WAY have the same life as a circus or zoo animal. That is a daft comparison.