The Buddhist doctrine of non-injury to living things is, of course, a natural consequence of the emphasis Buddhists place on the virtue of compassion. This is why most Buddhists are vegetarians.
Most of us non-Buddhists, however, are not vegetarians. So we believe, at least implicitly, that it is morally permissible to kill animals for meat, even though it causes a great deal of suffering to animals. Since this is the prevalent position, let me suggest brief considerations (besides the one listed in the question itself) in favor of the opposing view that it is not morally permissible to kill any living thing (even animals for meat).
Think of the following story I read in a newspaper article a couple of months ago. There was an incident in California, where a man was sent to jail for a few days. He had taken a turtle out of its shell, and bruised it, presumably for his own amusement. Veterinarians placed the poor abused turtle back within its shell, but it was afraid to poke its head out for quite a while. Evidently it felt scared and hurt.
I suppose it is debatable whether the man should have been sent to jail or not, for what he did to the turtle. But there is no debate that what he did to the animal was pretty bad (I suppose, but check what your own heart says), and he shouldn't have done it. But if we do believe this in the case of the turtle, why do we believe it is alright to make cows, pigs, chickens, etc. suffer in factory farms, just for our own culinary pleasure? Isn't there an inconsistency in our beliefs here?
It's not just...