So killing animals to grow veg is defensive killing?
Yes it is. In law and common morality, self-defence includes defence of property. It’s true that
killing a human to defend property is rightly generally considered disproportionate (US South notwithstanding) and it will often neither be necessary nor proportionate (and hence not justified) to kill field animals to defend crops.
To reiterate, I’m not justifying present practices of killing field animals in crop agriculture, rather I’m suggesting that it is not in the same moral category as breeding animals to exploit and kill. The ‘defence’ argument was one of several different arguments I presented to suggest a distinction. Alone perhaps it may not be compelling to everyone, but it should be seen as part of a cluster of arguments suggesting a distinction.
Now to address some of the challenges to the defence argument presented here.
First, there’s the argument that the animal ‘ends up dead either way’ so what’s the difference between the meat and crop industry? That response would be decisive if we were to embrace a consequentialist ethic which says the only thing that matters morally are consequences. But such a view is controversial and runs counter to most people’s views of ethics that are sensitive not only to outcomes but also the means by which outcomes are brought about. Our moral and legal systems distinguish between killing by acts and omissions, deliberate vs accidental killings and killings that are opportunistic/exploitative vs killings that are defensive. As such I think we have reason to doubt that all killings carry the same moral weight.
Second there’s the argument that in the human context the intent of the attacker renders the self-defence paradigm inapplicable to field animals who are just innocently doing what they need to survive. However, it’s not clear that the intention of the attacker is necessary to engage the right of self defence. In the self-defence literature there’s much discussion of so-called “innocent threats” - individuals who pose a threat to you through no fault of their own (e.g a sleep walker, somebody who had been drugged/hypnotised against their will, a hiker who has fallen of a cliff whilst attached by a rope to another climber, a toddler playing with a loaded gun, a heavy person who’s been pushed from a height etc.) There was a famous case in the early 2000s where one of the judges on the court of appeal found that doctors who performed an operation separating conjoined twins - and thereby killing the weaker one - would not commit murder because the weaker twin was an “innocent threat” slowly killing the other twin. So it’s not clear that the right to self-defence requires intent or culpability on behalf of the attacker, but even supposing it does, there’s still surely a difference between defending yourself from an innocent threat and inflicting violence on an individual who poses no threat to you whatsoever. We wouldn’t judge a human as harshly for defending themselves from an innocent threat as we would a straight up murderer or assaulter killing someone for money.
Third, to my mind the most serious challenge, the one relating to proportionality. Yes shooting a rabbit to stop them nibbling on lettuce can’t be justified. Self defence needs to meet at least 3 conditions to justified: (1) just cause, (2) necessity: (3) proportionality. Many killings of field animals to protect crops undoubtedly don’t meet criteria (2) & (3). But would it be possible to build an agricultural system with no such measures to control so-called “pests”? If such measures are needed to prevent failure of crop yields or the spread of disease then killing would be a proportionate response (if all reasonable alternatives were exhausted). In fact, we’re not really talking about property rights at all, we’re talking about basic needs like sustenance and bodily integrity. In a country like Britain there are no similarly weighty interests justifying animal product consumption, which really boils down to tradition, palate preference and convenience.
Finally, isn’t it better to kill animals to eat them rather than to simply eliminate the threat they pose? My view is no, not necessarily. Would it be better to kill a human in self-defence or kill them to extract their organs? Most, I suspect would say the former. Why would we say that? One reason might be because we view humans as having a certain dignity meaning it’s wrong to instrumentalise them in such a way. Many people also feel the same way about some animals - it would be wrong for people to shoot their pet dogs or cats to turn them into meat products, it’s wrong when people kill lions and elephants to turn them into trophies. Vegans extend this to cows, pigs, sheep and chickens too, that it’s wrong to treat them as mere resources to use. The animal eater can counter by identifying a morally relevant difference that justifies treating farmed animals differently from humans, dogs and lions in this respect. They may, for example, be tempted to say that farmed animals were bred to be killed, but if one thinks about that purported justification for more than a second they’d realise how weak it is and how many unappealing counter-examples it throws up.