Opponents of declawing state an obvious fact: if a declawed cat gets loose and is confronted with a dog (or a cat who has claws), he is practically defenseless. Vets who declaw cats strongly recommend to owners that the cats never be allowed to roam outside, since the outside world is an especially dangerous place for a declawed animal.
Owning a declawed cat does require some extra care and caution, but most people who choose declawing claim it is more than compensated for by the absence of shredded furniture.
Incidentally, many vets refuse to perform declawing on the back paws. Cats use their back claws to scratch themselves, and those back claws can help the cat climb a tree if he is being pursued by another animal.