Drawing lines can be difficult in any area of morality, and the more precise the line drawn, often the more difficulties that arise. However, the difficulty of drawing precise lines should not deter us from exploring less precise lines of minimum standards or moral baselines that are (or should be) reasonable for the vast majority of people in society, even if it would require a complete abolition of animal agriculture.
We establish and philosophically defend moral baselines regularly in society in the form of laws regarding such issues as murder, involuntary manslaughter, assault, declarations of war, and speed limits, even though these issues can be just as difficult to draw lines in as animal issues. None of us are “pure” when it comes to protecting humans from cruelty and death either; yet we do draw lines: we aren’t cannibals; and most of us don’t knowingly or happily support human enslavement and slaughter. 
We ought also to establish and philosophically defend such baselines regarding animals. Instead, we have a morally relative (and wrong) laissez-faire policy of refusing to even discuss line-drawing regarding animals, despite their overwhelming similarities to us in terms of the morally relevant characteristics: sentience and perceptual intelligence and awareness.
Given the morally relevant similarities and irrelevant differences between humans and other animals, and given that we are likely to find absolute perfection in non-harming far too ascetic or practically impossible in our modern society, veganism is the baseline we ought to promote and live by. Veganism is not the end point or the most we can do; rather, it is the least we can do.
Veganism is essentially refraining from contributing to the exploitation and intentional killing or slaughter of nonhuman beings. Preventing accidental and incidental human fatalities in traffic accidents and police action – even foreseen human deaths – is not required by laws prohibiting slavery and murder. In the same way, preventing accidental and incidental deaths in traffic accidents or harvesting crops – even foreseen deaths – is not required by veganism. In other words, abolitionist animal rights, as currently conceived, and the corresponding moral baseline of veganism are precisely the same in “line-drawing” as laws prohibiting chattel slavery and murder. Laws prohibiting slavery and murder say nothing about preventing motor vehicle injuries and fatalities, or how much cost we should incur in saving an injured child’s life, or “friendly fire” (unintended killing) in a justified war of self-defense. We should certainly take appropriate measures to reduce such deaths as much as possible, but again, veganism is merely a first and minimum standard, not the final or the best standard.
Choosing to consume animal products is a choice to partake in the exploitation and intentional slaughter of sentient beings. Given our wide variety of food choices today, we can easily refuse to partake in such exploitation and slaughter. In many cases, such as this one, drawing lines can be very appropriate and strongly defended, especially when one acknowledges that the line drawn is only a minimum standard of decency, not a maximum standard of purity.
 If you live and pay taxes in an industrialized nation with a strong military, such as the United States, you inadvertently and indirectly, and hopefully unwillingly and regrettably, support the slaughter of innocent humans in the form of warfare in other countries (waged primarily for economic reasons; the economic reasons controversially thought to be also ‘national security’ reasons) and arms supply to violent militias, just like vegans inadvertently, unwillingly, and regrettably support the slaughter of innocent nonhumans by living and paying taxes in our animal-exploiting society.
 I have edited this essay as of July 9, 2009 to remove two references to Jainism as suggesting an ascetic standard of non-violence. It was my previous understanding that many or most followers of Jainism went to ascetic lengths to avoid harming. I have since learned that this is not the case, and that, although veganism is increasing among followers of the religion, many are not vegans, much less practitioners of an ascetic form of non-violence.