I sometimes have to kill ants or other insects. I apologize to
   the insect(s) either before or after I do so. I don't know why I
   do that but I feel as if it's _something_.

   For ants, an "icky" barrier may help. Dichonateous Earth (DE) is
   like glass to insects when the step on it.. also can be
   dehydrating. They have pain sensors. If they do not move away
   when they feel the pain in order to survive... well... I
   apologize.

   Ants eating cat food: Ants have a right to eat. But... this
   restaurant discriminates against unacceptable life forms. They
   did not pay for this cat food. I did. I can choose to whom I
   feed it to as my cat paid for her meal. These ants did not pay.
   I ashamedly admit to utilizing capitalism to my advantage as
   justification for killing.

   I'm an American. Hard to escape one's upbringing.

   Having admitted all that... I might just let the ants eat after
   all, and move the bowl to a new location. If the ants can get at
   the cat food, then that means I left the restaurant in a bad
   neighborhood, susceptible to looting.

   Wow. No matter how I justify it, I just sound more and more like
   a bigot. *sigh*. Perfection? Nope. Far away from that am I.

   My cat wishes a pristine eating experience, to which the ants
   prove to be somewhat of a unwanted presence, and I must serve my
   master, even if her demands seem a little harsh.

   There. I've turned my cat into Hitler and I, the good German. I
   can handle that.