cats

If your cat isn't tagged so it can be returned to you, and you fined. And they have no way of knowing who that animal belongs to, if it carries any disease, how many animals it has killed, has it littered any bastards. Then yes, it should be put down.

The only problem there will be, would be you would be down one cat, sad for a while and likely get a new one.

Be a good owner, don't let the cat escape, and there won't be any 'problems'

:)