If one were to base their diet around moral responsibility, would eating only what the blade can cut be reasonable? Can it cut vegetables? Can animals be evil? Would training a cow to be evil in order to avoid starvation be morally justifiable?
Okay but if this became common enough that every paladin had a sword that only killed evil things and they also had the restriction that they had to only eat what they killed then it would be a good thing to raise evil creatures as food sources for the paladins, even though the people doing the raising are doing an evil thing.
You really need higher cognition for that, although I will grant that even cats on the higher end do understand that they are not supposed to be doing the thing they're about to do and will simply wait for you to look away or do it really really fast. They're just not capable of any greater evil that isn't running across the dinner table.
So now the question becomes how dedicated to evil does one have to be, in order to be evil? Does a life committed only to scratches and bodyslamming others out of the way of free food count, since it's a life committed only to selfish pursuits?