Btw, just because it might be of interest...
Vampire pumpkins and watermelons - Wikipedia, the free encyclopedia
Maybe in the Buffyverse, feeding the crops vampire (or other demon) blood could create them...though that's not how I'd explain them if I were to write them in (not that I have a definite idea offhand).
The idea of vampires creating "familiars" by feeding them at least some of their blood (not necessarily killing them in the process) is intriguing to me.
Not many people equate the killing of animals with killing of humans (though some are arbitrarily given more protection than others which varies nation to nation). I've even heard it argued that many predatory species won't eat their own kind (at least no more readily than humans will) so that there is some inherent morality there against killing your own species (though plenty of species will so I don't pay too much attention to that argument). As a rule of thumb, nature is set up vampiric, and nothing evolves that something doesn't evolve to eat it. That's just the way things are, and it's unnatural to refrain from that. Which isn't to say it's bad to refrain, mind you, just that it goes against the grain. And the slippery slope arguments can be made both ways, about if you're willing to eat X then why not X, or if it's wrong to kill X, then why not X? Other things have to be kept in mind, like protecting certain species unwisely can cause more harm than good for that and other species as it messes up the Balance and causes harm, including to the ones protected (this can even be true of protecting trees from natural forest fires), just as killing too many can.
Going by standard morality, eating animals is not amoral, at least not under normal circumstances, and animals are not held to the same standards as we are (which is why animals don't go to prison for killing each other or even not paying taxes, as they're considered incapable of living in a society, and thus any "social contract" excludes them, though laws can be put in place just as in the past laws have sometimes been put into place to protect slaves or others who are not considered citizens, or even possible citizens).
Though I'll throw in that the Master's "truly demonic concept of mass production" plan in the Wish did make me think of factory farms (whether such was intended or not).
That aside, drinking from willing donors would, of course, be more ethical, if it can be done. 'Course mystical drugs and all that muddy the issue a bit further.
