We have to look at it from another angle as well, my cats kill and I am not proud of it, but the farmer loves them for doing it because the rabbits ruin his crops, the mice destroy the hay, the rats destroy just about everything and the squirrels kill other wildlife like Dancer said. I truely didnt realise the impact that nature has until we lived on a farm, when we first moved into our house I found a magpie trap had been placed by the gamekeeper in the field out the back of our house, I was horrified and freed the poor magpie that was trapped inside, swore I was moving out and generally threw a hissy fit, but then after speaking with the gamekeeper and doing some research I find out that Magpies are one of the biggest killers of this countries lovely Song Birds, it is all meant to be and if mother nature hadnt intended cats to kill she wouldnt have given them the sharp teeth they have and the claws they have.
As Dawn says we have a massive population of Red Kites in our area and I am sure that the kills my cats make and leave are feeding most of that population !, the red kites are wonderful birds but they are not birds of prey and will only passive hunt which means they will only eat already dead animals, I get really upset about my cats killing animals but in all seriousness it probably is what keeps the Red Kites fed.