It's not so bad. We've killed most the native predators, so cats are the only thing keeping populations under control. And like most predators, they generally target sick and weak prey. And the cats are just trying to help fertilize your garden!
Yes, that wonderful, fertile cat shit full of Toxoplasma and other parasites. What a great addition to my garden! Not to mention that wonderful feeling and smell when your sink your hands into cat shit while prepping a garden bed.
Your other point, in regards to keeping populations under control, is way off the mark. http://www.nature.com/ncomms/journal/v4/n1/full/ncomms2380.h...
Keep your cats indoors, people! They're great pals to have, but inside.