He didn't kill the individual dog he ate, it would have died for food whether he ate it or not. On the other hand, because he did eat the dog, that means there is one less dog out there for food, so in a round-a-bout way, there is minus one dog out there. (unless of course somebody else ordered the pooch and he just grabbed a bite of the other guy's plate just to try it, in which case he had no affect on the overall population of dog)
I love dogs, but they are no different than a cow, horse or pig. I personally wouldn't eat one unless I was starving, but I don't think less of people for trying it. Different strokes and all that.
(apologies to Eraserhead if I read to much into "disgusting")
Come on now. Dogs are smarter than barnyard animals. That said, pigs are pretty smart. I gave up on bacon a while ago because it disturbs me to eat them too. Obviously, I wouldn't eat a horse either.
Cows however... I'd like to give up on eating them too, but that's a tough one.