Cats are urban terorrists. They kill thousands upon thousands of birds, small mammals, reptiles, and amphibians every year. People that own outdoor cats provide these animals with food but they still go out and kill, I ask why? The only answer I can come up with is "for fun". Wild animals hunt and kill when they are hungary and need food, not when their bellies are full.
I agree with M_surinamensis to a point, strays should be delt with in an appropriate mannar although I am hesitant to declare open season on them.