That's probably the reason Hog!
In the case of cats I'm pretty sure it's the connection to pets because I kill "vermin" without any trouble whatsoever. I laugh when I kill woodchucks and people have told me I'm sick because of that, but I would probably cry to kill a cat and people think there's something wrong with that.
Although, in the case of a truly wild cat I don't think I have any problems with it. The cats on my Grandfathers farm were "Semi-Domesticated", I guess Is the right word. You certainly couldn't touch them, but you could get within about 20 feet of them without them running away. They would tear you to shreds if you ever caught one.