Cats
Here's what I think of cats: as long as cats are outside, killing mice, eating birds, I don't really have a problem with them. I think that a cat's natural environment is outside. The problem I have with cats is when someone has fifteen or twenty (or even one, for that matter) cat inside their house, and I have to put up with smelling that cat, hearing that cat, and sneezing because of that cat.
Furthermore, I don't think cats are meant to be inside the house. Let's go over a few basic things that housepets should be able to do:
1) Come when they are called
2) Play fetch
3) Bark