I know a lot of people that would not own a cat that isn't declawed. I wonder what the net outcome is on cats being euthanized, I'm sure this will increase that number.
I had a girlfriend who wanted a cat but wanted to declaw the front claws, leaving the rear for defense if it ever got outside (I don't have a cat - this was her decision). The shelter explicitly forbade this, including a scary-looking legal contract promising not to declaw a cat, so she didn't adopt it in the end.
It's very likely the cat is now dead due to this policy since no one adopted it. I'm not sure that this outcome is more humane.