I'd prefer not to make animals suffer. I understand that you do not try to make them suffer either, you probably kill them as quick as possible--but I just cannot do it. I don't want to. Hell, when I walk through a grocery store and I see all the meat, I can't help but imagine the live animals and feel sick knowing they were slaughtered to be eaten by us.
And yes, that's the biggest reason why I'm vegetarian. Feel free to call me a wuss for it, I can't help it.
Commence photos of steak and comments saying "mmmm tasty meat"
But yeah, I've only ever killed (accidentally and not accidentally) mosquitos, flies, and small spiders. I even tend to try and catch flies and let them fly out of the window.