I'm actually not suggesting that we live on lettuce and you gave a good reason why it may actually do more harm to try, though the same damage is done when factory farms supplying McDonalds clear cut rain forests for grazing as would be done through agriculture but that's all a different debate. I guess my point is that we should attempt to do the least amount of harm. I think it is less harmfull, overall, to kill the mouse than the cat just as it's better to kill the cancer than the man. That being said, if there were no other food source then I guess a cat would work and if it was already dead then all the better.
As for the KFC, I'm down with boycotting it but not cuz I care about chickens. I boycott it already cuz it tastes like sh*t. If you want to boycott a company for inhumane activity then boycott all the fast food places plus Walmart and Nike for their inhumane treatment of their employees.
I feel a little light headed... maybe you should drive...