James McWilliams used to seem ok, but he is apparently a historian-turned-philosopher first and a feeling human being only second. The disembodied abstractions of utilitarianism always missed the point, whichever way they cut: The point is simple and obvious — but you need to have and use a heart to perceive it. Don’t hurt except if vitally necessary. You don’t need axiomatics to solemnly enumerate the actual, transitional and hypothetically imaginable cases of vital necessity. But nothing new follows from them. And certainly not carnivory or the meat industry.
Pain and pleasure are incommensurable (except for a blinkered utilitarian). No amount of pleasure justifies inflicting pain on others. (How much pain I choose to inflict on myself in exchange for my own pleasure is another matter, but irrelevant: this is about inflicting pain on OTHERS in exchange for MY pleasure — or for the pleasure of N of US, in utilitarian metrics.) The only faintly utilitarian moral truth is that we should try to minimize pain; but, again, pleasure is not part of the equation. And “don’t hurt except if vitally necessary” already covers that.
The Road-Kill Retort. I am astounded that anyone considers road-kills relevant to any serious discussion of veganism: Even if it is true that more animals are killed by roadway accidents than by hunting, the only decent response, it seems to me, and the one in keeping with the gravity of the topic of both animal suffering and roadway accidents, is not to treat roadway deaths as some sort of abstract and immutable given in some utilitarian debate but as a compelling reason to work on ways to reduce highway accidents (just as collateral animal deaths in vegetable farming should not be taken as an abstract, immutable given, but a compelling reason to work on ways to make vegetable farming more humane). Accidental road-kills are certainly not a scaleable, sustainable way to feed the world. And what is important is practical ethics, not hypothetical ethics.
Whenever a student raises the issue of road-kills as it were some sort of argument against veganism I immediately assure them that we are not talking about obsessive-compulsive disorder here: Anyone, vegan or not, is cordially invited to eat all the road kill they encounter and relish: it is of absolutely no consequence or relevance to anything whatsoever other than the need to improve highway safety for all. (But it is usually carnivores, not vegans, who prefer to keep the discussion focussed on abstractions rather than on the flesh and blood and terror and agony that are the real issue. But when a vegan is also an abstract ethical theorist….)