No, cats kill for fun, or at least they do so for reasons beyond securing their next meal. If you've had a cat, especially an 'outside cat,' you will know this to be true.
Watch your cat carefully the next time it catches an insect. The cat will eat it, eventually. But not after playing with it for a good few minutes. Cats are cruel. They bring their prey to the brink of death, then release it only to catch it few moments later and repeat the process.
A cat's jaw is delicate. The prey a cat normally choses has beaks or teeth or claws that can damage that jaw, causing infection. That could easily kill a cat. One possible reason that a cat "plays" with the prey is to minimise the risk of an injury near the jaw by wearing out the prey to the point that a killing bite can be given.
